Revenues and Business Information - Schedule of Geographical Distribution of Revenues and Assets (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	$ 231,700	$ 207,723	$ 523,006	$ 647,546
Total assets	806,237		806,237		$ 914,375
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	191,795	172,168	446,721	544,407
Total assets	682,534		682,534		756,053
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	31,729	30,651	54,450	67,983
Total assets	47,936		47,936		55,064
Rest of World
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	8,176	$ 4,904	21,835	$ 35,156
Total assets	$ 75,767		$ 75,767		$ 103,258