Schedule of Stock Activity Related to Share-Based Compensation (Detail)	12 Months Ended
	Dec. 31, 2012
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards expected to vest by period	43,687
Restricted Stock | 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards expected to vest by period	24,019
Restricted Stock | 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards expected to vest by period	12,354
Restricted Stock | 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards expected to vest by period	7,314
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards expected to vest by period	969,820
Restricted Stock Units (RSUs) | 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards expected to vest by period	475,689
Restricted Stock Units (RSUs) | 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards expected to vest by period	494,131