CONSOLIDATED BALANCE SHEETS (PARENTHETICAL) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 11,523,316	$ 11,897,639
Equity securities, available for sale, cost	$ 597,366	$ 575,776
Common shares, shares issued (in shares)	176,580	176,240
Common shares, shares outstanding (in shares)	86,441	96,066
Treasury shares (in shares)	90,139	80,174