Reserve for Claims and Claim Expenses (Schedule of Liability for Unpaid Claims and Claims Adjustment Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Net reserves as of January 1	$ 2,568,730	$ 2,632,519
Net incurred related to:
Current year	164,075	128,209
Prior years	29,006	(1,604)
Total net incurred	193,081	126,605
Net paid related to:
Current year	7,729	1,490
Prior years	147,500	124,411
Total net paid	155,229	125,901
Foreign exchange	2,287	11,072
Net reserves as of March 31	2,608,869	2,644,295
Reinsurance recoverable as of March 31	325,819	167,228
Gross reserves as of March 31	$ 2,934,688	$ 2,811,523