Comprehensive Income - AOCI (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	$ (51,357)	$ (87,936)
Other comprehensive income (loss) before reclassifications	(14,018)	58,563
Amounts reclassified from accumulated other comprehensive income (loss)	(33,932)	(21,984)
Other comprehensive income (loss), net of tax	(47,950)	36,579	$ (113,994)
Ending balance	(99,307)	(51,357)	(87,936)
Unrealized Gains (Losses) on Securities Available for Sale and Transferred to Held to Maturity
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	4,469	(31,490)
Other comprehensive income (loss) before reclassifications	(16,635)	61,284
Amounts reclassified from accumulated other comprehensive income (loss)	(44,160)	(25,325)
Other comprehensive income (loss), net of tax	(60,795)	35,959
Ending balance	(56,326)	4,469	(31,490)
Accumulated Gains (Losses) on Cash Flow Hedging Instruments
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	(7,189)	(5,289)
Other comprehensive income (loss) before reclassifications	2,672	(2,570)
Amounts reclassified from accumulated other comprehensive income (loss)	(1,861)	670
Other comprehensive income (loss), net of tax	811	(1,900)
Ending balance	(6,378)	(7,189)	(5,289)
Defined Benefit Plan Adjustment
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	(41,121)	(41,921)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	11,955	800
Other comprehensive income (loss), net of tax	11,955	800
Ending balance	(29,166)	(41,121)	(41,921)
Unamortized Impairment Losses on Investment Securities Held to Maturity
Accumulated Comprehensive Income [Roll Forward]
Beginning balance	(7,516)	(9,236)
Other comprehensive income (loss) before reclassifications	(55)	(151)
Amounts reclassified from accumulated other comprehensive income (loss)	134	1,871
Other comprehensive income (loss), net of tax	79	1,720
Ending balance	$ (7,437)	$ (7,516)	$ (9,236)