Other Comprehensive Income - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Net accumulated other comprehensive income:
Net unrealized gain on investment securities available-for-sale	$ (10,143)	$ 684
Net actuarial loss on defined benefit post-retirement benefit plans	2,038	(378)
Accumulated Other Comprehensive Income (Loss), Cumulative Changes in Net Gain (Loss) from Cash Flow Hedges, Effect Net of Tax	(23)	100
Net accumulated other comprehensive income	$ (8,128)	$ 406