Income Taxes (Details) - Entity [Domain] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Income Taxes
Tax expense	$ 23,942	$ 20,161	$ 38,826	$ 34,804
Overall effective income tax expense rate (as a percent)	36.00%	38.60%	36.00%	38.50%
Net deferred tax assets	$ 84,400		$ 84,400		$ 91,800
Valuation allowance against deferred tax assets	$ 0		$ 0		$ 0
Federal
Income Taxes
Period of NOL carryforward			20 years
Period of federal tax credit carryforwards			20 years
State | Minimum
Income Taxes
Period of NOL carryforward			10 years
State | Maximum
Income Taxes
Period of NOL carryforward			20 years