Notes Receivable from Employees - Additional information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 Note	Dec. 31, 2013 Note	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Notes outstanding	311	340
Amortization of forgivable loan expense	$ 32.1	$ 35.1	$ 32.8