Stockholders' Equity - Additional Information (Detail) - TREASURY STOCK, AT COST: - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Treasury stock, shares retired	0	1,400	4,600
Purchases, shares	0	1,380	3,850