Operating Segments - Geographic Segments (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, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Revenues	$ 72,095	$ 75,526	$ 72,822	$ 64,856	$ 57,661	$ 56,440	$ 50,080	$ 47,774	$ 285,299	$ 211,955	$ 166,806
Long-Lived Assets	94,639				87,909				94,639	87,909	75,377
United States
Segment Reporting Information [Line Items]
Revenues									255,256	181,743	138,510
Long-Lived Assets	80,617				79,301				80,617	79,301	70,208
Other
Segment Reporting Information [Line Items]
Revenues									30,043	30,212	28,296
Long-Lived Assets	$ 14,022				$ 8,608				$ 14,022	$ 8,608	$ 5,169