Reserve for Claims and Claim Expenses (Schedule of Liability for Unpaid Claims and Claims Adjustment Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves as of January 1	$ 2,632,519	$ 1,345,816	$ 1,462,705
Net incurred related to:
Current year	694,957	610,685	341,745
Prior years	(164,126)	(162,447)	(143,798)
Total net incurred	530,831	448,238	197,947
Net paid related to:
Current year	83,015	95,747	39,830
Prior years	506,279	425,565	241,286
Total net paid	589,294	521,312	281,116
Amounts acquired	0	1,394,117	0
Foreign exchange	(5,326)	(34,340)	(33,720)
Net reserves as of December 31	2,568,730	2,632,519	1,345,816
Reinsurance recoverable as of December 31	279,564	134,526	66,694
Gross reserves as of December 31	$ 2,848,294	$ 2,767,045	$ 1,412,510