Equity Based Compensation - Summary of Stock Option Activity for Periods Indicated (Detail) (USD $)	3 Months Ended
	Sep. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options outstanding	11,953	12,703	18,703	28,203	12,703	30,003	30,003	30,003
Weighted- average exercise price	$ 92.89	$ 93.86	$ 93.65	$ 90.79	$ 93.86	$ 91.72	$ 91.72	$ 91.72
Stock options outstanding , Forfeited	750	6,000	9,500	1,800
Weighted - average exercise price, Forfeited	$ 109.20	$ 93.20	$ 85.16	$ 106.40