Quarterly report pursuant to Section 13 or 15(d)

HELD-TO-MATURITY SECURITIES - Contractual Maturities (Details)

v3.8.0.1
HELD-TO-MATURITY SECURITIES - Contractual Maturities (Details) - USD ($)
$ in Thousands
Sep. 30, 2017
Dec. 31, 2016
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months $ 307,053 $ 186,226
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Amortized Cost 8,688,399 7,806,939
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value 8,655,805 7,787,268
Federal agencies: Mortgage-backed securities    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 301,637 186,226
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, Under 1 year 0 0
Held-to-maturity Securities, 1-5 years 0 0
Held-to-maturity Securities, 6-10 years 68,668 41,261
Held-to-maturity Securities, Over 10 years 8,067,957 7,157,083
Amortized Cost 8,136,625 7,198,344
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 0 0
Fair Value, 1-5 years 0 0
Fair Value, 6-10 years 68,478 40,791
Fair Value, Over 10 years 8,035,777 7,139,943
Fair Value 8,104,255 7,180,734
Federal agencies, Other agencies    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 0 0
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, Under 1 year 0 0
Held-to-maturity Securities, 1-5 years 0 0
Held-to-maturity Securities, 6-10 years 375,580 398,341
Held-to-maturity Securities, Over 10 years 170,628 204,083
Amortized Cost 546,208 602,424
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 0 0
Fair Value, 1-5 years 0 0
Fair Value, 6-10 years 376,393 399,452
Fair Value, Over 10 years 169,741 201,180
Fair Value 546,134 600,632
Total U.S. Treasury, Federal agency securities    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 301,637 186,226
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Amortized Cost 8,682,833 7,800,768
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value 8,650,389 7,781,366
Municipal securities    
Schedule of Held-to-maturity Securities [Line Items]    
Over 12 Months 5,416 0
Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract]    
Held-to-maturity Securities, Under 1 year 0 0
Held-to-maturity Securities, 1-5 years 0 0
Held-to-maturity Securities, 6-10 years 0 0
Held-to-maturity Securities, Over 10 years 5,566 6,171
Amortized Cost 5,566 6,171
Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract]    
Fair Value, Under 1 year 0 0
Fair Value, 1-5 years 0 0
Fair Value, 6-10 years 0 0
Fair Value, Over 10 years 5,416 5,902
Fair Value $ 5,416 $ 5,902