Nature of Operations and Basis of Presentation - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pre-tax
Net unrealized securities gains (losses)	$ (8,381)	$ (4,885)	$ (23,443)
Interest rate swaps	(754)	(525)	0
Pension and other postretirement benefit plan adjustments	(8,255)	(6,696)	(5,068)
Accumulated other comprehensive loss	(17,390)	(12,106)	(28,511)
After-tax
Net unrealized securities gains (losses)	(5,176)	(3,017)	(14,476)
Interest rate swaps	(466)	(324)	0
Pension and other postretirement benefit plan adjustments	(5,097)	(4,134)	(3,129)
Accumulated other comprehensive loss	$ (10,739)	$ (7,475)	$ (17,605)