Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($)	Jun. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Available for sale securities, amortized cost	$ 3,830,737,000	$ 3,814,847,000
Allowance for expected credit losses	553,000	0
Trading securities, cost	46,349,000	43,914,000
Equity investments at fair value, cost	161,562,000	211,356,000
Other investments, portion carried at fair value	92,204,000	98,611,000
Premium receivable, allowance for credit loss	$ 7,906,000	$ 7,436,000
Common shares, par value (in usd per share)	$ 0.01	$ 0.01
Common shares, shares authorized (in shares)	100,000,000	100,000,000
Common shares, shares issued (in shares)	63,422,426	63,308,741
Deferred tax expense (benefit) on accumulated other comprehensive income (loss)	$ (63,367,000)	$ 4,423,000
Treasury shares, number of shares (in shares)	9,325,180	9,325,180