Income Taxes - Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the differences between taxes on income (loss) before income taxes
Taxes (benefit) on U.S. and other international earnings (losses) at greater than the Bermuda rate		$ (98,119)	$ (181,426)	$ (109,101)
Increase (decrease) in valuation allowance		29,165	17,865	22,655
Impact of Tax Reform Act		138,635
Tax reserves and interest		(148,615)	(3,468)	(12,679)
State income taxes (benefit)		(4,036)	(19,802)	1,087
Total income tax expense (benefit)		$ (82,970)	$ (186,831)	$ (98,038)
Effective tax rate (as a percent)		14.30%	15.60%	22.90%
Release of reserves due to favorable audit outcomes		$ 167,000
Effective income tax rate		35.00%
Provision to income tax expense		$ 138,600
Forecast
Reconciliation of the differences between taxes on income (loss) before income taxes
Effective income tax rate	21.00%
Office of the Tax Commissioner, Bermuda
Reconciliation of the differences between taxes on income (loss) before income taxes
Effective income tax rate		0.00%