Retirement Plans - Net Periodic Pension Cost (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Pension plan [Member]
Cost components:
Service cost	$ (284)	$ (251)	$ (239)
Interest cost	(375)	(384)	(316)
Expected return on plan assets	454	446	342
Net amortization and deferral	190	220	186
Total net periodic pension cost	395	409	399
SERP [Member]
Cost components:
Service cost	(525)	172	223
Interest cost	(208)	215	226
Net amortization and deferral	287	(66)	0
Total net periodic pension cost	$ 1,020	$ (453)	$ (449)