Income Taxes (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Net Deferred Tax Liability
Deferred tax liabilities	$ 1,668,655		$ 1,423,173
Deferred tax assets	1,239,916		985,356
Less: valuation allowance	(53,735)	[1]	(48,077)	[1]
Net deferred tax assets	1,186,181		937,279
Net deferred tax liability	$ 482,474		$ 485,894

[1] The valuation allowance is related to state net operating losses and bonus depreciation, general business credits and charitable contributions.