Revenues and Business Information - Schedule of Geographical Distribution of Revenues and Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	$ 220,405	$ 172,149	$ 439,823	$ 345,407
Total assets	727,476		727,476		$ 699,068
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	193,557	150,704	372,239	289,106
Total assets	600,040		600,040		519,933
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	13,896	16,637	37,332	38,656
Total assets	33,765		33,765		83,834
Rest of World
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	12,952	$ 4,808	30,252	$ 17,645
Total assets	$ 93,671		$ 93,671		$ 95,301