Consolidated Statements of Comprehensive Income - AOCI - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss)	$ (12,521)	$ (12,534)	$ 10,937
Accumulated Unrealized Loss on Securities Available- for-Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(10,271)	(2,950)	(20,419)
Other comprehensive income (loss)	(12,374)	(7,321)	17,469
Ending balance	(22,645)	(10,271)	(2,950)
Accumulated Unrealized Loss on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(2,468)	(1,138)	0
Other comprehensive income (loss)	1,292	(1,330)	(1,138)
Ending balance	(1,176)	(2,468)	(1,138)
Unrecognized Net Pension Costs
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(15,650)	(11,767)	(6,373)
Other comprehensive income (loss)	(1,439)	(3,883)	(5,394)
Ending balance	(17,089)	(15,650)	(11,767)
Total Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(28,389)	(15,855)	(26,792)
Other comprehensive income (loss)	(12,521)	(12,534)	10,937
Ending balance	$ (40,910)	$ (28,389)	$ (15,855)