Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended
	Nov. 30, 2012
Significant Accounting Policies [Line Items]
Stock dividend payable date	Dec. 24, 2012
stock dividend date of record	Dec. 10, 2012
Common Class A
Significant Accounting Policies [Line Items]
Stock split ratio for 100 percent of stock dividend declared	2
Common Class B
Significant Accounting Policies [Line Items]
Stock split ratio for 100 percent of stock dividend declared	2