Retirement Plans - Net Periodic Pension Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension plan
Cost components:
Service cost	$ (265)	$ (248)	$ (359)
Interest cost	(466)	(392)	(402)
Expected return on plan assets	615	576	542
Net amortization and deferral	(284)	(45)	(253)
Settlement recognition	(536)	(407)	0
Total net periodic pension cost	(936)	(516)	(472)
SERP
Cost components:
Service cost	0	(26)	(318)
Interest cost	(278)	(258)	(219)
Net amortization and deferral	(337)	(23)	(229)
Total net periodic pension cost	$ (615)	$ (307)	$ (766)