Accumulated Other Comprehensive Income (Loss) - Changes in components of AOCI - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	$ (3,871)	$ (377)	$ (9,723)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(5,004)	(4,617)	8,682
Amounts reclassified from accumulated other comprehensive income (loss)	664	1,123	664
Other comprehensive income (loss), net of tax	(4,340)	(3,494)	9,346
Balance at the end of the period	(8,211)	(3,871)	(377)
Benefit plans
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(6,015)	(5,315)	(3,585)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(749)	(1,332)	(2,201)
Amounts reclassified from accumulated other comprehensive income (loss)	569	632	471
Other comprehensive income (loss), net of tax	(180)	(700)	(1,730)
Balance at the end of the period	(6,195)	(6,015)	(5,315)
Unrealized gain and losses on sales of available for sale securities
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	2,588	5,467	(5,573)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(4,221)	(3,181)	11,039
Amounts reclassified from accumulated other comprehensive income (loss)	(75)	302	1
Other comprehensive income (loss), net of tax	(4,296)	(2,879)	11,040
Balance at the end of the period	(1,708)	2,588	5,467
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss)
Balance at the beginning of the period	(444)	(529)	(565)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(34)	(104)	(156)
Amounts reclassified from accumulated other comprehensive income (loss)	170	189	192
Other comprehensive income (loss), net of tax	136	85	36
Balance at the end of the period	$ (308)	$ (444)	$ (529)