Accumulated Other Comprehensive Income Components of Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ (38,449)	$ (22,017)
Other comprehensive loss before reclassifications	4,273	17,026
Amounts reclassified from accumulated other comprehensive income (loss)	(376)	(146)
Ending Balance	(34,552)	(5,137)
Unrealized Gains (Losses) on Investment Securities Not Other-Than-Temporarily Impaired
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(23,047)	(6,499)
Other comprehensive loss before reclassifications	4,273	17,026
Amounts reclassified from accumulated other comprehensive income (loss)	(719)	(616)
Ending Balance	(19,493)	9,911
Unrealized Non-Credit Gains (Losses) on Other-Than-Temporarily Impaired Debt Securities
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	273	458
Other comprehensive loss before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Ending Balance	273	458
Unrealized Effective Portions of Losses on Forward-Starting Interest Rate Swaps
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	0	(15)
Other comprehensive loss before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	4
Ending Balance	0	(11)
Unrecognized Pension and Postretirement Plan Income (Costs)
Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(15,675)	(15,961)
Other comprehensive loss before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	343	466
Ending Balance	$ (15,332)	$ (15,495)