Stock Based Compensation - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2012 Y
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance metric	100.00%
Performance metric, minimum	0.00%
Performance metric, maximum	133.00%
Average period based on relative TSR (in years)	3
Performance And Market-Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance metric, minimum	0.00%
Performance metric, maximum	150.00%