Executive Nonqualified Defined Benefit Plan - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Vesting period	6 years
Discount rate for benefit obligation and net periodic service cost	3.25%	4.00%	5.25%
Insurance policy value	$ 1,466	$ 1,102
Percentage of employee contributions	50.00%
Percentage of employee compensation	2.00%
W.E.T.
Defined Benefit Plan Disclosure [Line Items]
Underfunded defined benefit plan	3,844	3,152
Chief Executive Officer [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual retirement payment	$ 300,000