Stockholders' Equity - Summary of the Companys Change in the Common Stock (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Outstanding shares of voting common stock at the beginning of year	37,728,857
Exercise of stock options	165,340	256,622	1,511,207
Outstanding shares of voting common stock at the end of year	37,318,722	37,728,857
Voting Common Stock [Member]
Class of Stock [Line Items]
Outstanding shares of voting common stock at the beginning of year	39,224,000	38,902,000	37,725,000
Exercise of stock options	120,000	256,000	1,498,000
Issuance of restricted stock, net of shares withheld for tax payments and cancellations	116,000	66,000	(321,000)
Outstanding shares of voting common stock at the end of year	39,460,000	39,224,000	38,902,000