Compensation Plans Employee Stock Purchase Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Compensation plans
Number of shares of common stock available for grant	5,900,000
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 of common stock available for grant	1,600,000
Issuance of common stock under Employee Stock Purchase Plan (in shares)	199,464	186,665	218,135
Proceeds from issuance of shares under incentive and share-based compensation plans, excluding stock options	$ 3,200,000	$ 2,600,000	$ 4,200,000
Risk free interest rate	1.80%	0.90%	0.40%
Dividend yield	0.40%	0.50%	0.40%
Volatility factor of the expected market price of the Company's common stock	55.90%	62.50%	95.00%
Expected life (in years)	6 months	6 months	6 months
Stock-based compensation expense	$ 1,100,000	$ 1,000,000	$ 2,000,000