Insurance Activity - Additional Information (Detail) - USD ($) $ in Millions		9 Months Ended
	Aug. 31, 2009	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Effects of Reinsurance [Line Items]
Quoted percentage to share base	50.00%
Balances in the fair market reserve		$ 9.8		$ 12.5
Decreased value of fair market reserve		$ 2.7	$ 30.3
WMMRC [Member]
Effects of Reinsurance [Line Items]
Second loss layer risk percentage of range minimum	5.00%
Second loss layer risk percentage of range maximum	10.00%
First loss layer risk percentage of range minimum	4.00%
First loss layer risk percentage of range maximum	5.00%
Minimum period of reinsurance agreements		5 years
Maximum period of reinsurance agreements		10 years
WMMRC [Member] | Minimum [Member] | Credit Concentration Risk | Liabilities, Total [Member]
Effects of Reinsurance [Line Items]
Net of ceding commission, percentage	25.00%
WMMRC [Member] | Maximum [Member] | Credit Concentration Risk | Liabilities, Total [Member]
Effects of Reinsurance [Line Items]
Net of ceding commission, percentage	40.00%