Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Millions								3 Months Ended		9 Months Ended
	Nov. 05, 2015	Sep. 14, 2015	Aug. 06, 2015	Jun. 15, 2015	May. 07, 2015	Mar. 26, 2015	Feb. 27, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	May. 19, 2015	May. 18, 2015	Dec. 31, 2014
Dividends Payable [Line Items]
Common stock, shares authorized								100,000,000		100,000,000		100,000,000	50,000,000	50,000,000
Dividends per share (in dollars per share)			$ 0.13		$ 0.13		$ 0.13	$ 0.13	$ 0.11	$ 0.39	$ 0.33
Cash payment amount		$ 3.0		$ 3.0		$ 3.0				$ 9.1	$ 7.7
Common stock available for future share repurchases, amount								$ 11.7		$ 11.7
Common stock repurchased, number of shares repurchased								49,511	47,717	148,419	130,917
Common stock repurchased, average price per share (in dollars per share)								$ 60.59	$ 48.89	$ 60.63	$ 40.82
Common stock repurchased, total repurchase costs								$ 3.0	$ 2.4	$ 9.0	$ 5.3
Subsequent Event
Dividends Payable [Line Items]
Dividends per share (in dollars per share)	$ 0.16