Summary of Significant Accounting Policies - Restricted Cash and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted Cash
Total restricted cash outstanding	$ 770	$ 600
Allowance for doubtful accounts:
Beginning balance	69	883	$ 959
Add: bad debt recovery	(116)	(87)	(16)
Less: write-offs and other adjustments	50	(727)	(60)
Ending balance	$ 3	69	$ 883
Accounts receivable write-off		$ 666