Other Comprehensive Income - Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in net unrealized Gain during period:
Change in net unrealized gain during period, before tax amount	$ (19,379)	$ 3,151	$ 27,522
Change in net unrealized gain during period, tax expense (benefit)	(7,625)	1,240	10,830
Change in net unrealized gain during period, net of tax amount	(11,754)	1,911	16,692
Investment securities available-for-sale:
Reclassification adjustment for net gains included in net income, before tax amount	(330)	(137)	(61)
Reclassification adjustment for net, gains included in net income, tax expense (benefit)	(130)	(54)	(24)
Reclassification adjustment for net gains included in net income, net of tax amount	(200)	(83)	(37)
Unamortized Premium on Available-For-Sale Securities Transferred to Held-To-Maturity
Unamortized premium on available-to-sale securities transferred into held-for-maturity, before tax amount	1,858	1,611	(6,923)
Unamortized premium on available-to-sale securities transferred into held-for-maturity, tax expense (benefit)	731	634	(2,725)
Unamortized premium on available-to-sale securities transferred into held-for-maturity, net of tax amount	1,127	977	(4,198)
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	(203)	165
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	(80)	65
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax	(123)	100
Change in net actuarial loss:
Change in net actuarial loss, before tax amount	3,983	58	1,731
Change in net actuarial loss, tax expense (benefit)	1,567	23	681
Change in net actuarial loss, net of tax amount	2,416	35	1,050
Other comprehensive income (Loss)
Other comprehensive income (loss), before tax	(14,071)	4,848	22,269
Total other comprehensive income, tax expense (benefit)	(5,537)	1,908	8,762
Other comprehensive income, net of tax	$ (8,534)	$ 2,940	$ 13,507