Deferred Compensation Retirement Plans - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2008 Chairman Of The Board And Chief Executive Officer [Member]	Dec. 31, 2014 Chairman Of The Board And Chief Executive Officer [Member] Subsequent Event [Member]	Dec. 31, 2008 President And Chief Operating Officer [Member]	Dec. 31, 2014 President And Chief Operating Officer [Member] Subsequent Event [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Annual retirement benefit				$ 1,333,333		$ 1,214,333
Retirement benefit biannual increase					1,666,666		1,547,666
Annual retirement benefit, maximum annual benefit					2,000,000		1,881,000
Discount rate used in present value calculation	5.00%	5.50%
Annual retirement benefit, accrued expense liability	$ 4,300,000	$ 3,200,000	$ 3,200,000