CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 11,043,394	$ 11,523,316
Equity securities, available for sale, cost	$ 563,110	$ 597,366
Common shares, shares issued (in shares)	176,580	176,580
Common shares, shares outstanding (in shares)	83,157	86,441
Treasury shares, shares (in shares)	93,423	90,139