Revenue Recognition - Accounts Receivable and Deferred Revenue (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Assets
Accounts receivable	$ 60,397	$ 44,089
Liabilities:
Deferred revenue, current portion	1,156	1,420
Deferred revenue, long-term portion	36,850
Total deferred revenues	38,006	1,420
Other noncurrent assets	3,446	$ 3,979
Evercord
Liabilities:
Deferred revenue, long-term portion	$ 2,500
Evercord | Storage services
Liabilities:
Prepayment plan, delivery duration (in years)	18 years
Accounts receivable	$ 2,600
Other noncurrent assets	$ 300
Evercord | Storage services | Alternate
Liabilities:
Prepayment plan, financing duration (in months)	12 months
Evercord | Storage services | Minimum
Liabilities:
Prepayment plan, financing duration (in months)	6 months
Evercord | Storage services | Maximum
Liabilities:
Prepayment plan, financing duration (in months)	18 months