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 6 Months Ended
Jun. 30, 2017
Jun. 30, 2017
Jun. 30, 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   42,404 92,797
Amounts reclassified from accumulated OCI to earnings   8,255 (681)
Period change     92,116
Balance, end of period $ 10,654,182 10,654,182 7,507,304
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   42,801 82,145
Amounts reclassified from accumulated OCI to earnings   6,375 (1,783)
Period change 49,176   80,362
Balance, end of period (143,588) (143,588) 88,723
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   0 110
Amounts reclassified from accumulated OCI to earnings   0 0
Period change 0   110
Balance, end of period 287 287 286
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   (397) 10,542
Amounts reclassified from accumulated OCI to earnings   641 (579)
Period change 244   9,963
Balance, end of period (2,390) (2,390) 6,015
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   1,239 1,681
Period change 1,239   1,681
Balance, end of period (204,666) (204,666) (229,066)
Accumulated Other Comprehensive Loss      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Balance, beginning of period   (401,016) (226,158)
Period change 50,659    
Balance, end of period $ (350,357) (350,357) (134,042)
Reclassification out of Accumulated Other Comprehensive Income      
AOCI Attributable to Parent, Net of Tax [Roll Forward]      
Net unrealized loss on securities transfer   $ (98,000) $ (82,000)