Consolidated Statements of Comprehensive Income - AOCI - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income	$ 646	$ 13,348
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	1,977	10,795
Ending balance	(20,668)	524
Accumulated Unrealized Gain (Loss) on Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(1,176)	(2,468)
Other comprehensive income	(1,331)	2,553
Ending balance	(2,507)	85
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	646	13,348
Ending balance	$ (40,264)	$ (15,041)