Schedule II. Condensed Financial Information Of Registrant (Balance Sheets) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets
Fixed maturity investments trading, at fair value - amortized cost $22,402 at December 31, 2016 (2015 - $96,957)	$ 6,891,244	$ 6,765,005
Short term investments, at fair value	1,368,379	1,208,401
Cash and cash equivalents	421,157	506,885	$ 525,584	$ 408,032
Investments in subsidiaries	0	0
Accrued investment income	38,076	39,749
Receivable for investments sold	105,841	220,834
Other assets	175,382	181,011
Goodwill and other intangible assets	251,186	265,154
Total assets	12,352,082	11,555,287
Liabilities
Due to subsidiaries	0	0
Payable for investments purchased	305,714	391,378
Other liabilities	301,684	245,145
Total liabilities	6,309,911	5,777,139
Shareholders' Equity
Preference shares: $1.00 par value – 16,000,000 shares issued and outstanding at December 31, 2016 (2015 – 16,000,000)	400,000	400,000
Common shares: $1.00 par value – 41,187,413 shares issued and outstanding at December 31, 2016 (2015 – 43,701,064)	41,187	43,701
Additional paid-in capital	216,558	507,674
Accumulated other comprehensive income	1,133	2,108
Retained earnings	4,207,699	3,778,701
Total shareholders’ equity	4,866,577	4,732,184	3,865,715
Total liabilities, noncontrolling interests and shareholders’ equity	12,352,082	11,555,287
Parent Company
Assets
Fixed maturity investments trading, at fair value - amortized cost $22,402 at December 31, 2016 (2015 - $96,957)	22,119	96,441
Short term investments, at fair value	365,155	253,451
Cash and cash equivalents	7,067	10,185	$ 5,986	$ 8,796
Investments in subsidiaries	4,074,769	3,902,519
Due from subsidiaries	7,413	19,168
Dividends due from subsidiaries	0	62,114
Accrued investment income	105	1,253
Receivable for investments sold	136	26
Other assets	410,757	390,302
Goodwill and other intangible assets	130,407	137,064
Total assets	5,017,928	4,872,523
Liabilities
Notes and bank loans payable	117,000	117,000
Due to subsidiaries	14,644	2,641
Payable for investments purchased	0	999
Other liabilities	19,707	19,699
Total liabilities	151,351	140,339
Shareholders' Equity
Preference shares: $1.00 par value – 16,000,000 shares issued and outstanding at December 31, 2016 (2015 – 16,000,000)	400,000	400,000
Common shares: $1.00 par value – 41,187,413 shares issued and outstanding at December 31, 2016 (2015 – 43,701,064)	41,187	43,701
Additional paid-in capital	216,558	507,674
Accumulated other comprehensive income	1,133	2,108
Retained earnings	4,207,699	3,778,701
Total shareholders’ equity	4,866,577	4,732,184
Total liabilities, noncontrolling interests and shareholders’ equity	$ 5,017,928	$ 4,872,523