Lease and Financing Obligations (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
New Building [Abstract]
Deposit paid to landlord	$ 29,957,000	$ 24,406,000
Typical term of lease renewal options	3 years
Minimum future operating lease obligations [Abstract]
2015	29,382,000
2016	24,980,000
2017	21,396,000
2018	18,285,000
2019	12,183,000
Thereafter	678,000
Total	106,904,000
Minimum future financing obligations [Abstract]
2015	386,000
2016	673,000
2017	693,000
2018	714,000
2019	735,000
Thereafter	4,382,000
Total minimum lease payments	7,583,000
Rent expense for operating leases	52,300,000	34,600,000	27,700,000
Interest expense associated with financing obligation	0	0	0
Lease Agreement for New Regional Headquarters Building [Member]
New Building [Abstract]
Construction-in-progress	13,100,000
Financing obligation of other long term liabilities	10,400,000
Deposit paid to landlord	2,700,000
Additional project costs associated with construction of New Building to be recognized	8,600,000
Additional financing obligation associated with construction of building to be recognized	1,300,000
Additional deposits to be paid to landlord associated with construction of building	7,300,000
Tenant incentive asset	6,400,000
Deferred tenant incentive liability	$ 6,400,000