Stock Based Compensation - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance metric for performance based restricted stock units	100.00%
Performance metric for performance based restricted stock units minimum potential range	0.00%
Performance metric for performance based restricted stock units maximum potential range	200.00%
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]
Market-based awards granted to senior management	79,850	99,500
Performance metric, minimum	0.00%
Performance metric, maximum	150.00%
Performance And Market-Based Restricted Stock Units | Senior management
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Market-based awards granted to senior management	76,175	90,250
Performance-Based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase as grant in period, percentage	100.00%
Decrease as forfeited, percentage	100.00%