Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUES OF ASSETS AND LIABILITIES - Significant Unobservable Level 3 Inputs (Details)

v3.4.0.3
FAIR VALUES OF ASSETS AND LIABILITIES - Significant Unobservable Level 3 Inputs (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2016
Dec. 31, 2015
Fair Value Disclosures [Abstract]    
Available-for-sale and other securities $ 9,319,381 $ 8,775,441
Fair Value, Measurements, Recurring    
Fair Value Disclosures [Abstract]    
MSRs 14,819 17,585
Available-for-sale and other securities 8,985,921 8,442,655
Automobile loans 1,216 1,748
Fair Value, Measurements, Recurring | Level 3    
Fair Value Disclosures [Abstract]    
MSRs 14,819 17,585
Gross amounts of recognized assets 11,082 6,721
Gross amounts of recognized liabilities 735 665
Available-for-sale and other securities 2,376,072 2,195,888
Automobile loans 1,216 1,748
Fair Value, Measurements, Nonrecurring    
Fair Value Disclosures [Abstract]    
Impaired loans Fair Value Disclosure   62,029
Accrued income and other assets Fair Value Disclosure   27,342
Asset-backed Securities | Fair Value, Measurements, Recurring    
Fair Value Disclosures [Abstract]    
Available-for-sale and other securities 837,374 861,413
Asset-backed Securities | Fair Value, Measurements, Recurring | Level 3    
Fair Value Disclosures [Abstract]    
Available-for-sale and other securities 94,329 100,337
Municipal securities    
Fair Value Disclosures [Abstract]    
Available-for-sale and other securities 2,633,756 2,456,396
Municipal securities | Fair Value, Measurements, Recurring    
Fair Value Disclosures [Abstract]    
Available-for-sale and other securities 2,633,756 2,456,396
Municipal securities | Fair Value, Measurements, Recurring | Level 3    
Fair Value Disclosures [Abstract]    
Available-for-sale and other securities $ 2,281,743 $ 2,095,551
Cost Approach Valuation Technique | Maximum | MSRs | Level 3    
Fair Value Disclosures [Abstract]    
Constant prepayment rate 26.50% 25.70%
Spread over forward interest rate swap rates 0.092 0.092
Cost Approach Valuation Technique | Maximum | Private label CMO | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 7.80% 7.20%
Cumulative default 56.00% 50.00%
Loss given default 80.00% 80.00%
Cost Approach Valuation Technique | Maximum | Asset-backed Securities | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 11.40% 10.90%
Cumulative prepayment rate 100.00% 100.00%
Cumulative default 100.00% 100.00%
Loss given default 100.00% 100.00%
Cure given deferral 75.00% 75.00%
Cost Approach Valuation Technique | Maximum | Automobile Loan | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 5.00% 5.00%
Cost Approach Valuation Technique | Minimum | MSRs | Level 3    
Fair Value Disclosures [Abstract]    
Constant prepayment rate 7.00% 7.90%
Spread over forward interest rate swap rates 0.033 0.033
Cost Approach Valuation Technique | Minimum | Private label CMO | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 0.60% 0.30%
Cumulative default 0.10% 0.10%
Loss given default 5.00% 5.00%
Cost Approach Valuation Technique | Minimum | Asset-backed Securities | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 4.90% 4.60%
Cumulative prepayment rate 0.00% 0.00%
Cumulative default 1.50% 1.60%
Loss given default 85.00% 85.00%
Cure given deferral 0.00% 0.00%
Cost Approach Valuation Technique | Minimum | Automobile Loan | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 0.20% 0.20%
Cost Approach Valuation Technique | Weighted Average | MSRs | Level 3    
Fair Value Disclosures [Abstract]    
Constant prepayment rate 12.30% 14.70%
Spread over forward interest rate swap rates 0.054 0.054
Cost Approach Valuation Technique | Weighted Average | Private label CMO | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 3.50% 3.10%
Cumulative default 2.90% 2.10%
Loss given default 21.80% 20.50%
Cost Approach Valuation Technique | Weighted Average | Asset-backed Securities | Level 3    
Fair Value Disclosures [Abstract]    
Discount rate 6.50% 6.20%
Cumulative prepayment rate 9.60% 9.60%
Cumulative default 11.10% 11.10%
Loss given default 96.70% 96.60%
Cure given deferral 36.50% 36.80%
Cost Approach Valuation Technique | Weighted Average | Automobile Loan | Level 3    
Fair Value Disclosures [Abstract]    
Constant prepayment rate 154.20% 154.20%
Discount rate 2.30% 2.30%
Life of pool cumulative losses 2.10% 2.10%
Market Approach Valuation Technique | Maximum | Derivative Instruments [Member] | Level 3    
Fair Value Disclosures [Abstract]    
Net market price 22.10% 20.90%
Estimated Pull through % 99.80% 99.80%
Market Approach Valuation Technique | Minimum | Derivative Instruments [Member] | Level 3    
Fair Value Disclosures [Abstract]    
Net market price (2.50%) (3.20%)
Estimated Pull through % 22.10% 11.90%
Market Approach Valuation Technique | Weighted Average | Derivative Instruments [Member] | Level 3    
Fair Value Disclosures [Abstract]    
Net market price 2.30% 1.90%
Estimated Pull through % 79.40% 76.70%