Summary of Significant Accounting Policies - Deferred Costs & Impairment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Significant Accounting Policies
Impairment loss related to intangible assets	$ 0	$ 0	$ 0
Goodwill	41,191,000	41,191,000
Impairment loss related to goodwill	0	0	0
Deferred Costs
Internal sales commissions	18,748,000	17,558,000
Third party commissions	13,643,000	15,866,000
External legal counsel	730,000	718,000
Total	33,121,000	34,142,000
Recoverability of Long-Lived Assets
Impairment of real estate	$ 0	$ 0	$ 0