Income Taxes - Income Tax Reconciliation (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of Income Tax Expense
Expected provision at federal statutory tax rate	35.00%	35.00%	35.00%
State tax expense, net of federal benefit	1.00%	1.70%	2.10%
Income tax credits	(0.40%)	0.00%	(0.10%)
Other	0.50%	0.70%	0.90%
Total income tax expense (benefit)	36.10%	37.40%	37.90%