Equity Based Compensation - Summary of Information Regarding Stock Option Under Plan that are Outstanding and Exercisable (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options outstanding and exercisable	11,953
Weighted- average exercise price	$ 92.89
Weighted- average remaining contractual life (years)	1 year 2 months 27 days
Range one [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options outstanding and exercisable	5,503
Weighted- average exercise price	$ 80.00
Weighted- average remaining contractual life (years)	22 days
Exercise price or range of exercise prices	$ 80.00
Range two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options outstanding and exercisable	2,500
Weighted- average exercise price	$ 94.52
Weighted- average remaining contractual life (years)	10 months 28 days
Exercise price or range of exercise prices, minimum	$ 93.20
Exercise price or range of exercise prices, maximum	$ 106.40
Range three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock options outstanding and exercisable	3,950
Weighted- average exercise price	$ 109.83
Weighted- average remaining contractual life (years)	3 years 1 month 2 days
Exercise price or range of exercise prices, minimum	$ 109.20
Exercise price or range of exercise prices, maximum	$ 121.60