Stockholders' Equity - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
	Nov. 25, 2014	Dec. 31, 2014	Dec. 31, 2013	Aug. 18, 2014
Schedule Of Capitalization Equity [Line Items]
Amount approved under share purchase program	$ 20,000,000			$ 10,000,000
Additional share amount added to repurchase program	10,000,000
Aggregate purchase price of repurchased shares		12,543,000
Class A common stock
Schedule Of Capitalization Equity [Line Items]
Common stock, voting rights per share		$ 1
Cash dividend paid per share		$ 0.10	$ 0.125
Cash dividend paid per share amount		8,900,000	11,000,000
Number of shares repurchased		2,500,000
Average price of repurchased shares		$ 5.08
Aggregate purchase price of repurchased shares		12,500,000
Class B common stock
Schedule Of Capitalization Equity [Line Items]
Common stock, voting rights per share		$ 10
Cash dividend paid per share		$ 0.10	$ 0.125
Cash dividend paid per share amount		8,900,000	11,000,000
Class U common stock
Schedule Of Capitalization Equity [Line Items]
Cash dividend paid per share		$ 0.10	$ 0.125
Cash dividend paid per share amount		$ 8,900,000	$ 11,000,000