Summary of Significant Accounting Policies - Deferred Costs & Impairment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Summary of Significant Accounting Policies
Impairment loss related to intangible assets	$ 0	$ 0
Goodwill	40,646		$ 40,646
Impairment loss related to goodwill	0	0
Deferred Costs
Amortization of initial direct costs	3,300	3,400
Internal sales commissions	15,335		15,064
Third party commissions	12,820		10,845
Other	436		462
Total	28,591		$ 26,371
Recoverability of Long-Lived Assets
Impairment of long-lived assets	$ 0	$ 0