Deferred Commission (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Capitalized Contract Cost [Line Items]
Deferred commissions	$ 20,200,000		$ 19,300,000
Deferred commissions amortization	3,500,000	$ 2,600,000
Deferred commissions impairment	$ 0	$ 0
Minimum
Capitalized Contract Cost [Line Items]
Sales commissions amortization period	3 years		1 year
Maximum
Capitalized Contract Cost [Line Items]
Sales commissions amortization period	7 years		2 years