Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets
Fixed maturities, at amortized cost or cost	$ 5,874,140	$ 5,876,261
Short-term investments, at amortized cost or cost	3,638,995	3,381,714
Other investments, at amortized cost or cost	331,950	330,416
Investments in investment affiliates, at cost	$ 75,302	$ 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	162,003,969	161,994,491	161,285,411	161,279,976
Common shares, shares outstanding	79,329,028	79,319,550	79,137,590
Treasury shares, common shares	82,674,941	82,674,941	82,147,821