Stockholders' Equity (Details) $ in Millions	1 Months Ended		9 Months Ended
	May. 31, 2015 USD ($)	May. 31, 2014 USD ($)	Sep. 30, 2015 USD ($) item shares	Sep. 30, 2014 USD ($) shares	Dec. 31, 2014 shares
Stockholders' equity
Shares acquired by the entity			2,200	3,000
Cost of shares acquired by the entity | $			$ 0.2	$ 0.1
Authorized shares of common stock			100,000,000
Voting rights per common share | item			1
Common stock, outstanding shares			16,730,000		16,748,000
2014 Stock Purchase Plan
Stockholders' equity
Period over which repurchases allowed under the plan		12 months
Common stock purchased under the stock purchase plan (in shares)			60,900	0
Cost of shares of common stock acquired | $			$ 3.4
2014 Stock Purchase Plan | Maximum
Stockholders' equity
Authorized amount of repurchase under the stock purchase plan | $		$ 25.0
2015 Stock Purchase Plan
Stockholders' equity
Period over which repurchases allowed under the plan	12 months
Common stock purchased under the stock purchase plan (in shares)			42,100
Cost of shares of common stock acquired | $			$ 2.4
2015 Stock Purchase Plan | Maximum
Stockholders' equity
Authorized amount of repurchase under the stock purchase plan | $	$ 25.0