Schedule II. Condensed Financial Information Of Registrant (Balance Sheets Parenthetical) (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Fixed maturity investments trading, Amortized cost	$ 6,920,690		$ 6,825,877
Preference Shares, Par Value (In dollars per share)	$ 1		$ 1
Preference Shares, Shares issued (In shares)	16,000,000		16,000,000
Preference shares, Shares outstanding (In shares)	16,000,000		16,000,000
Common Shares, Par Value (In dollars per share)	$ 1		$ 1
Common Shares, Shares issued (In shares)	41,187,413		43,701,064
Common Shares, Shares outstanding (In shares)	41,187,413		43,701,064
Parent Company
Condensed Financial Statements, Captions [Line Items]
Fixed maturity investments trading, Amortized cost	$ 22,402		$ 96,957
Preference Shares, Par Value (In dollars per share)		$ 1.00		$ 1.00
Preference Shares, Shares issued (In shares)		16,000,000		16,000,000
Preference shares, Shares outstanding (In shares)		16,000,000		16,000,000
Common Shares, Par Value (In dollars per share)		$ 1.00		$ 1.00
Common Shares, Shares issued (In shares)		41,187,413		43,701,064
Common Shares, Shares outstanding (In shares)		41,187,413		43,701,064