Income Taxes - Reconciliation of Federal Income Tax Rate to Company's Effective Income Tax Rate (Details)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Effective income tax rate    
Federal income tax rate 35.00% 35.00%
Tax credits, net of equity adjustment (3.00%) 0.00%
Permanent differences (1.00%) (2.00%)
Effective income tax rate 31.00% 33.00%