Retirement Plans - Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Total changes	$ (407)	$ 0	$ 0
Pension plan
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net (gain)/loss	2,973	(1,867)
Recognition of net actuarial gain or (loss)	(481)	(282)
Recognized prior service cost	29	28
Total changes	2,521	(2,121)
Changes, net of taxes	1,511	(1,271)
SERP
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net (gain)/loss	1,399	(745)
Recognition of net actuarial gain or (loss)	(23)	(229)
Total changes	1,376	(974)
Changes, net of taxes	$ 826	$ (584)