Stockholders' Equity - Common Stock Purchased Including Purchase of Common Stock for Tax Withholdings (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Equity [Abstract]
Shares purchased (shares)	263,000	36,542	501,782	127,792	0	0	572,550	0	16,719	13,884	65,791	291,861	929,116	572,550	388,255
Amount	$ 3,446	$ 558	$ 7,520	$ 1,922	$ 0	$ 0	$ 10,000	$ 0	$ 274	$ 228	$ 1,078	$ 4,893	$ 13,446	$ 10,000	$ 6,473