Income Taxes - Income before taxes by jurisdiction (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	$ 844,247	$ 742,505	$ 589,387
Bermuda
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	794,926	717,661	609,710
United States
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	53,055	87,032	9,600
Other
Income Tax Disclosure [Line Items]
Income (loss) before income taxes	$ (3,734)	$ (62,188)	$ (29,923)