Income Taxes - Reconciliation of Federal Income Tax Rate to Company's Effective Income Tax Rate (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2014
Sep. 30, 2013
Sep. 30, 2014
Sep. 30, 2013
Effective income tax rate        
Federal income tax rate 35.00% 35.00% 35.00% 35.00%
Tax credits, net of equity adjustment (1.00%) 0.00% (2.00%) (1.00%)
Permanent differences (1.00%) (1.00%) (1.00%) (1.00%)
Effective income tax rate 33.00% 34.00% 32.00% 33.00%