Compensation Plans Employee Stock Purchase Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation plans
Number of shares available for grant	2,800,000
Employee Stock Purchase Plan [Member]
Compensation plans
Maximum employee subscription rate	15.00%
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Employee Subscription	$ 25,000
Percent of offering date price paid	85.00%
Number of shares available for grant	900,000
Issuance of common stock under Employee Stock Purchase Plan (in shares)	197,214	83,136	77,427
Proceeds from Issuance of Shares under Incentive and Share-based Compensation Plans, Excluding Stock Options	$ 4,800,000	$ 4,100,000	$ 3,700,000
Risk free interest rate	0.10%	0.10%	0.10%
Dividend yield	0.20%	0.10%	0.20%
Volatility factor of the expected market price of the Company's common stock	61.20%	33.00%	41.10%
Expected life (in years)	6 months	6 months	6 months
Stock-based compensation expense	$ 1,800,000	$ 1,100,000	$ 1,100,000