Summary of Significant Accounting Policies - Deferred Costs & Impairment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Summary of Significant Accounting Policies
Impairment loss related to intangible assets	$ 0	$ 0	$ 0	$ 0
Goodwill	40,646		40,646		$ 41,191
Impairment loss related to goodwill	0	0	0	0
Reduction of goodwill			500
Deferred Costs
Internal sales commissions	17,352		17,352		18,748
Third party commissions	12,104		12,104		13,643
External legal counsel	776		776		730
Total	30,232		30,232		$ 33,121
Recoverability of Long-Lived Assets
Impairment of real estate	$ 0	$ 0	$ 0	$ 0