Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Fixed maturities - available for sale, at market value, amortized cost	$ 13,213,596	$ 12,831,159
Equity securities - available for sale, at market value, cost	147,512	148,326
Other invested assets, at cost	$ 665,153	$ 601,925
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	68,555,000	68,336,000
Accumulated other comprehensive income (loss), net of deferred income tax expense (benefit)	$ 20,968	$ 20,715
Treasury shares	24,363,000	23,650,000
Long Term Subordinated Notes [Member]
Debt instrument, stated interest rate	6.60%	6.60%
Debt instrument, maturity date	May 01, 2067
4.868% Senior notes due 6/1/2044 [Member] | Senior Notes [Member]
Debt instrument, stated interest rate	4.868%	4.868%
Debt instrument, maturity date	Jun. 01, 2044