Stockholders' Equity - Repurchase Activities (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity [Abstract]
Number of shares repurchased (in shares)	131,669	99,210	131,669	188,126
Average price per share (in dollars per share)	$ 27.74	$ 37.77	$ 27.74	$ 38.52
Total repurchase costs	$ 3.6	$ 3.7	$ 3.6	$ 7.2