Quarterly report pursuant to Section 13 or 15(d)

OTHER COMPREHENSIVE INCOME OTHER COMPREHENSIVE INCOME - AOCI Roll Forward (Details)

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OTHER COMPREHENSIVE INCOME OTHER COMPREHENSIVE INCOME - AOCI Roll Forward (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Balance, beginning of period $ 10,308,146 $ 6,594,606
Other comprehensive income before reclassifications 5,535 58,751
Amounts reclassified from accumulated OCI to earnings 4,621 121
Period change   58,872
Balance, end of period 10,437,147 7,157,670
Unrealized gains and (losses) on debt securities | Debt Securities    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Balance, beginning of period (192,764) 8,361
Other comprehensive income before reclassifications 6,725 49,434
Amounts reclassified from accumulated OCI to earnings 3,797 (300)
Period change 10,522 49,134
Balance, end of period (182,242) 57,495
Unrealized gains and (losses) on debt securities | Equity Securities    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Balance, beginning of period 287 176
Other comprehensive income before reclassifications 0 68
Amounts reclassified from accumulated OCI to earnings 0 0
Period change 0 68
Balance, end of period 287 244
Unrealized gains and (losses) on cash flow hedging derivatives    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Balance, beginning of period (2,634) (3,948)
Other comprehensive income before reclassifications (1,190) 9,249
Amounts reclassified from accumulated OCI to earnings 364 (420)
Period change (826) 8,829
Balance, end of period (3,460) 4,881
Unrealized gains (losses) for pension and other post- retirement obligations    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Balance, beginning of period (205,905) (230,747)
Other comprehensive income before reclassifications 0 0
Amounts reclassified from accumulated OCI to earnings 460 841
Period change 460 841
Balance, end of period (205,445) (229,906)
Accumulated Other Comprehensive Loss    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Balance, beginning of period (401,016) (226,158)
Period change 10,156  
Balance, end of period (390,860) (167,286)
Reclassification out of Accumulated Other Comprehensive Income    
AOCI Attributable to Parent, Net of Tax [Roll Forward]    
Net unrealized loss on securities transfer $ (81,000) $ (82,000)