Lease and Financing Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
New Building [Abstract]
Deposit paid to landlord	$ 39,016	$ 29,957
Value of New Building	666,130	636,711
Accumulated depreciation	211,593	171,928
Operating Leases, Minimum Future Obligations [Abstract]
2016	36,627
2017	29,970
2018	24,201
2019	16,221
2020	8,927
Thereafter	1,921
Total	117,867
Financing Obligations, Minimum Future Obligations [Abstract]
2016	630
2017	649
2018	669
2019	689
2020	709
Thereafter	3,290
Total minimum lease payments	6,636
Rent expense for operating leases	52,400	52,300	$ 34,600
Interest expense associated with financing obligation	$ 100	0	$ 0
New Regional Headquarters Building [Member]
New Building [Abstract]
Extension period for lease	10 years
Initial term of lease	10 years
Construction-in-progress		13,100
Financing obligation	$ 10,600	10,400
Deposit paid to landlord	9,300	2,700
Value of New Building	19,900
Accumulated depreciation	300
Tenant incentive asset	5,600	6,400
Deferred tenant incentive liability	$ 5,100	$ 6,100
Office Space and Computer Hardware [Member]
New Building [Abstract]
Extension period for lease	3 years