Stockholders' Equity - Stock Repurchase Program (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	6 Months Ended
	Jul. 30, 2018	Jun. 30, 2018	Jun. 30, 2017
Stockholders’ Equity
Shares repurchased during the period (in shares)	550,141	4,065,160	2,416,089
Average purchase price per share for share repurchase (in dollars per share)		$ 17.82	$ 16.74
Aggregate purchase price	$ 9,900	$ 72,463	$ 40,444
Remaining authorized repurchase amount		$ 63,800