Stockholders' Equity - Summary of the Companys Change in the Common Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Outstanding shares of voting common stock at the beginning of year	37,620,736
Exercise of stock options	120,588	380,967	195,410
Outstanding shares of voting common stock at the end of year	37,639,917	37,620,736
Voting Common Stock [Member]
Class of Stock [Line Items]
Outstanding shares of voting common stock at the beginning of year	37,621,000	37,544,000	37,409,000
Exercise of stock options	121,000	262,000	181,000
Issuance of restricted stock, net of shares withheld for withholding tax payments and cancellations	22,000	39,000	104,000
Repurchases	(124,000)	(224,000)	(150,000)
Outstanding shares of voting common stock at the end of year	37,640,000	37,621,000	37,544,000