Retirement Plans - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Total changes	$ (536)	$ (407)	$ 0
Pension plan
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net (gain) loss	(482)	2,973
Recognition of net actuarial gain or (loss)	(849)	(481)
Recognized prior service cost	29	29
Total changes	(1,302)	2,521
Changes, net of taxes	(781)	1,511
SERP
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net (gain) loss	726	1,399
Recognition of net actuarial gain or (loss)	337	(23)
Total changes	1,063	1,376
Changes, net of taxes	$ 638	$ 826