Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) ft² RenewalOption	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Operating Leased Assets [Line Items]
Lease expiration date	Feb. 28, 2023
Rent expense	$ 2,500	$ 4,200	$ 3,700
Total cash receipts from subleases	29,200
Future minimum lease payments under operating leases [Abstract]
2018	5,547
2019	5,645
2020	3,175
2021	910
2022	827
2023 and thereafter	136
Total minimum lease payments	$ 16,240
Corporate Headquarters and Call Center [Member]
Operating Leased Assets [Line Items]
Area of leased property | ft²	264,000
Area of leased property, sublease | ft²	221,000
Number of renewal options | RenewalOption	2
Renewal options period	5 years
Operating lease term	15 years
Tenant improvement allowance	$ 10,700
Corporate Headquarters and Call Center [Member] | Minimum [Member]
Operating Leased Assets [Line Items]
Rent expense	4,300
Corporate Headquarters and Call Center [Member] | Maximum [Member]
Operating Leased Assets [Line Items]
Rent expense	$ 6,600
Office Space in Chandler [Member]
Operating Leased Assets [Line Items]
Area of leased property | ft²	92,000
Lease expiration date	Apr. 30, 2020
Office Space In Ashburn [Member]
Operating Leased Assets [Line Items]
Area of leased property | ft²	6,000