Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 Vote	Dec. 31, 2012
Class A common stock [Member]
Schedule of Capitalization, Equity [Line Items]
Common stock, voting rights per share	1
Cash dividend paid per share	$ 0.125	$ 0.120
Cash dividend paid per share amount	$ 11.0	$ 10.3
Class B common stock [Member]
Schedule of Capitalization, Equity [Line Items]
Common stock, voting rights per share	10
Cash dividend paid per share	$ 0.125	$ 0.120
Cash dividend paid per share amount	11.0	10.3
Class U common stock [Member]
Schedule of Capitalization, Equity [Line Items]
Cash dividend paid per share	$ 0.125	$ 0.120
Cash dividend paid per share amount	$ 11.0	$ 10.3