Stockholders' Equity - Dividends (Details) $ / shares in Units, $ in Millions											12 Months Ended
	Feb. 28, 2017 $ / shares	Dec. 15, 2016 USD ($)	Nov. 04, 2016 $ / shares	Sep. 15, 2016 USD ($)	Aug. 08, 2016 $ / shares	Jun. 15, 2016 USD ($)	May 25, 2016	May 09, 2016 $ / shares	Mar. 28, 2016 USD ($)	Feb. 24, 2016 $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($) $ / shares
Class of Stock [Line Items]
Two-for-one stock split							2
Dividends declared (in dollars per share)			$ 0.09		$ 0.08			$ 0.08		$ 0.08	$ 0.33	$ 0.285	$ 0.23
Dividends paid (in dollars per share)											$ 0.33	$ 0.29	$ 0.23
Cash payment amount | $		$ 4.2		$ 3.8		$ 3.7			$ 3.8		$ 15.5	$ 12.8	$ 10.7
Subsequent Event
Class of Stock [Line Items]
Dividends declared (in dollars per share)	$ 0.09