Consolidated Statements of Comprehensive Income - AOCI - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income	$ 2,874	$ 14,987
Accumulated Unrealized Gain (Loss) on Securities Available- for-Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(22,645)	(10,271)
Other comprehensive income	4,586	12,348
Ending balance	(18,059)	2,077
Accumulated Unrealized Gain (Loss) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,176)	(2,468)
Other comprehensive income	(1,712)	2,639
Ending balance	(2,888)	171
Unrecognized Net Pension Costs
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(17,089)	(15,650)
Other comprehensive income	0	0
Ending balance	(17,089)	(15,650)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(40,910)	(28,389)
Other comprehensive income	2,874	14,987
Ending balance	$ (38,036)	$ (13,402)