Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Fixed maturities - available for sale, at amortized cost	$ 12,708,891	$ 12,391,164
Equity securities - available for sale, at cost	156,000	148,342
Other invested assets, at cost	485,771	508,447
Preferred shares, par value	$ 0.01	$ 0.01
Preferred shares, authorized	50,000,000	50,000,000
Preferred shares, issued	0	0
Preferred shares, outstanding	0	0
Common shares, par value	$ 0.01	$ 0.01
Common shares, authorized	200,000,000	200,000,000
Common shares, outstanding	68,171,000	67,965,000
Accumulated other comprehensive income (loss), deferred income tax expense (benefit)	$ 65,137	$ 57,661
Treasury shares	22,114,000	20,422,000
Senior Notes [Member]
Debt instrument, stated interest rate	5.40%	5.40%
Debt instrument, maturity date	Oct. 15, 2014	Oct. 15, 2014
Long Term Subordinated Notes [Member]
Debt instrument, stated interest rate	6.60%	6.60%
Debt instrument, maturity date	May 01, 2067	May 01, 2067