Summary of Significant Accounting Policies - Deferred Costs & Impairment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Costs
Internal sales commissions	$ 17,558	$ 13,171
Third party commissions	15,866	13,665
External legal counsel	718	393
Total	34,142	27,229
Recoverability of Long-Lived Assets
Impairment of real estate	0	0	$ 0
Impairment loss related to intangible assets	0	0	0
Goodwill	41,191	41,191
Impairment loss related to goodwill	0	0	$ 0
Allowance for doubtful accounts (in dollars)	$ 56	$ 112