Stockholders' Equity - Additional Information (Detail) - 2016 Share Repurchase Program [Member] - USD ($)	3 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Nov. 30, 2016
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, authorized amount				$ 200,000,000
Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of common stock	0	34,200,000	34,200,000
Treasury stock acquired, average cost per share		$ 2.70	$ 2.70
Stock repurchase program, aggregate number of shares repurchased value		$ 92,900,000	$ 92,900,000