CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 11,242,063	$ 11,523,316
Equity securities, available for sale, cost	$ 591,559	$ 597,366
Common shares, shares issued (in shares)	176,580	176,580
Common shares, shares outstanding (in shares)	85,170	86,441
Treasury shares, shares (in shares)	91,410	90,139