Loss and Loss Adjustment Expenses - Summary Exposures to Various Asbestos Related Claims (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Asbestos Claims [Line Items]
Reserves for loss and LAE at beginning of year	$ 570,450	$ 538,214	$ 532,204
Incurred losses and LAE during the current year	228,973	219,903	189,706
Less loss and LAE payments for claims occurring during the current year	44,474	50,423	53,213
Reserves for loss and LAE	614,557	570,450	538,214
Asbestos Issue [Member]
Asbestos Claims [Line Items]
Reserves for loss and LAE at beginning of year	167
Incurred losses and LAE during the current year	53	168
Less loss and LAE payments for claims occurring during the current year	1	1
Reserves for loss and LAE	$ 219	$ 167