Executive Compensation Plan (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Schedule Of Executive Compensation Plan [Line Items]
Deferred executive compensation plan, grant date value of awards	$ 1,600,000	$ 1,800,000	$ 1,100,000
Deferred executive compensation plan, net expense	1,719,000	1,477,000	1,134,000
Deferred executive compensation plan, estimated future expense for unvested awards year one	1,500,000
Deferred executive compensation plan, estimated future expense for unvested awards year two	544,000
Deferred executive compensation plan, estimated future expense for unvested awards year three	$ 136,000