Stockholders' Equity - Share Repurchase Program (Details) - Share repurchase program December 2013 - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2013
Shareholders' Equity
Total purchases authorized under share repurchase program			$ 150,000,000
Shares repurchased	518,576
Average purchase price (in dollars per share)	$ 15.81
Amount of remaining authorization to repurchase common stock		$ 64,100,000