Liability for Loss and LAE - Activity in the Liability for Loss and Loss Adjustment Expense (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Activity in liability for loss and loss adjustment expense
Reserves as of January 1		$ 14,357,635	$ 12,970,600
Less: reinsurance recoverables	[1]	2,026,100	1,703,700
Net reserves as of January 1		12,331,500	11,266,900
Other adjustments		(100)	0
Incurred loss and LAE, net of reinsurance, related to:
Current year		995,100	1,168,200
Prior years		(53,300)	(56,100)
Total incurred loss and LAE, net of reinsurance		941,787	1,112,070
Paid loss and LAE, net of reinsurance, related to:
Current year	[2]	68,200	87,400
Prior years	[2]	902,100	766,800
Total paid loss and LAE, net of reinsurance	[2]	970,300	854,200
Foreign currency exchange rate effect		(8,800)	29,500
Net reserves as of March 31		12,294,100	11,554,300
Reinsurance recoverables as of March 31	[1]	2,022,300	1,738,700
Reserves as of March 31		$ 14,316,367	$ 13,293,000

[1] Reinsurance recoverables in this table include only ceded loss and LAE reserves.

[2] Includes paid losses and LAE, net of reinsurance, related to commutations.