Significant Accounting Policies - Revenue (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017	Jan. 01, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Accumulated deficit	$ (677,320,000)		$ (665,584,000)	$ (667,357,000)
Revenues	99,403,000	$ 117,518,000
Total revenues	99,403,000	117,518,000
Revenue recognized	5,500,000
Unamortized balance of deferred commissions	800,000
Capitalized contract cost, amortization	100,000
Capitalized contract cost, impairment	0
United States
Disaggregation of Revenue [Line Items]
Total revenues	89,389,000	106,528,000
Caribbean
Disaggregation of Revenue [Line Items]
Total revenues	1,137,000	947,000
Canada
Disaggregation of Revenue [Line Items]
Total revenues	2,286,000	1,512,000
Europe
Disaggregation of Revenue [Line Items]
Total revenues	1,227,000	1,577,000
Other
Disaggregation of Revenue [Line Items]
Total revenues	5,364,000	$ 6,954,000
Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Accumulated deficit			$ 1,800,000
Revenues	$ 1,200,000