Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Assets
Fixed maturities, at amortized cost or cost	$ 5,651,953	$ 5,876,261
Short-term investments, at amortized cost or cost	3,728,930	3,381,714
Other investments, at amortized cost or cost	341,883	330,416
Investments in investment affiliates, at cost	$ 72,135	$ 61,944
Preferred shares - Shareholders' Equity
Preferred shares, shares issued	16,000	16,000
Preferred shares, shares outstanding	16,000	16,000
Common Shares - Shareholders' Equity
Common shares, shares issued	163,186,889	161,994,491	161,934,355	161,279,976
Common shares, shares outstanding	80,511,948	79,319,550	79,518,581
Treasury shares, common shares	82,674,941	82,674,941	82,415,774