Employee Benefit Plans - Savings and Retirement Plan (Details) (Defined Contribution Savings and Retirement Plan [Member], USD $)	0 Months Ended	1 Months Ended	12 Months Ended
	Jan. 31, 2009	Apr. 30, 2012	Dec. 31, 2012 investment_funds	Dec. 31, 2011	Dec. 31, 2010
Defined Contribution Savings and Retirement Plan Disclosure [Line Items]
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	6.00%
Employer matching contribution, percent			50.00%
Number of funds to invest in for defined contribution plan			19
Defined Contribution Plan, Vesting Period			5 years
Contribution expense			$ 10,000,000	$ 38,000	$ 100,000
Employer annual cap per participant		600
Employer annual cap per participant as pro-rated for 2012			450
Expense adjustment for savings and retirements plans			13,000,000
Deferred credits and other [Member]
Defined Contribution Savings and Retirement Plan Disclosure [Line Items]
Defined Contribution Savings and Retirement Plans, Liabilities, Noncurrent			$ 32,000,000	$ 20,700,000