Incremental Costs to Obtain a Contract with a Customer (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Commission and incentive payments
Capitalized Contract Cost [Line Items]
Total deferred costs	$ 56,098		$ 58,580
Commission and incentive payments | Deferred costs included in prepaid and other current assets
Capitalized Contract Cost [Line Items]
Total deferred costs	34,786		35,044
Commission and incentive payments | Deferred costs included in other assets
Capitalized Contract Cost [Line Items]
Total deferred costs	21,312		$ 23,536
Deferred commissions
Capitalized Contract Cost [Line Items]
Amortization expense	$ 10,900	$ 9,100