Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Operating Loss Carryforwards [Line Items]
Total income tax expense (benefit)	$ 107,418		$ 183,358
Effective income tax rate	18.30%		42.40%
Available-for-sale Securities, Income Tax Expense on Change in Unrealized Holding Gain (Loss)			$ 0
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Provisional charge for re-measurement of U.S. deferred tax assets due to US Tax Reform		$ 326,200