Revenues and Business Information - Schedule of Geographical Distribution of Revenues and Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	$ 153,523	$ 220,405	$ 291,306	$ 439,823
Total assets	714,769		714,769		$ 914,375
United States
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	132,246	193,557	254,926	372,239
Total assets	591,860		591,860		756,053
Europe
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	16,005	13,896	22,721	37,332
Total assets	34,376		34,376		55,064
Rest of World
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues	5,272	$ 12,952	13,659	$ 30,252
Total assets	$ 88,533		$ 88,533		$ 103,258