Non-Marketable Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Carrying value of the Company's non-marketable investments	$ 5.7	$ 6.6
Gain (losses) from non-marketable investments	(0.6)	0.1	(0.4)
Book value of investment	0.9	1.2
Gross distributions received from funds	0.4	0.5	0.5
Bonus paid under cash bonus plan	$ 0
Cash bonus plan expiration date	Jun. 30, 2015
Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Participant in the cash bonus plan	10
Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Ownership interest of company	5.00%