Changes in Performance-Based RSU Outstanding (Detail) (Performance Based Restricted Stock)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Performance Based Restricted Stock
Schedule of Share based Compensation Arrangements by Share based Payment Award, Equity Instruments, Other Than Options, Restricted Stock Units [Line Items]
Balance at beginning of year	1,174,492	1,023,492	872,027
Granted	653,355	521,423	449,100
Awarded	(260,175)	(309,656)	(252,551)
Forfeited	(141,434)	(60,767)	(45,084)
Balance at end of year	1,426,238	1,174,492	1,023,492