Insurance Activity - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 19, 2012	Aug. 31, 2009
Effects of Reinsurance [Line Items]
Quoted percentage to share base					50.00%
Balances in the fair market reserve	$ 12,500,000	$ 46,300,000
Loss contract fair market value reserve	12,549,000	46,319,000		63,100,000
Decreased value of fair market reserve	$ 33,800,000	$ 5,900,000	$ 10,900,000
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]
Effects of Reinsurance [Line Items]
Net of ceding commission, percentage					25.00%
WMMRC [Member] | Maximum [Member]
Effects of Reinsurance [Line Items]
Net of ceding commission, percentage					40.00%