Incremental Costs to Obtain a Contract with a Customer (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Commission and incentive payments
Capitalized Contract Cost [Line Items]
Total deferred costs	$ 58,234		$ 58,234		$ 58,580
Commission and incentive payments | Deferred costs included in prepaid and other current assets
Capitalized Contract Cost [Line Items]
Total deferred costs	36,162		36,162		35,044
Commission and incentive payments | Deferred costs included in other assets
Capitalized Contract Cost [Line Items]
Total deferred costs	22,072		22,072		$ 23,536
Deferred commissions
Capitalized Contract Cost [Line Items]
Amortization expense	$ 10,800	$ 8,900	$ 21,700	$ 18,000