Deferred Contract Costs - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Capitalized contract cost, net	$ 15,300,000		$ 13,200,000
Capitalized contract cost, amortization	400,000	$ 100,000
Impairment losses	0	$ 0
Prepaid expenses and other current assets
Capitalized Contract Cost [Line Items]
Capitalized contract cost, net	1,900,000		1,600,000
Other Assets
Capitalized Contract Cost [Line Items]
Capitalized contract cost, net	$ 13,400,000		$ 11,600,000