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Stockholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Apr. 30, 2018
Nov. 30, 2016
2018 Share Repurchase Program [Member] | Common Class A [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Repurchase of common stock 0 0      
2018 Share Repurchase Program [Member] | Common Class A [Member] | Maximum [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Stock repurchase program, authorized amount       $ 200,000,000.0  
2016 Share Repurchase Program [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Treasury stock acquired, average cost per share     $ 3.59    
Stock repurchase program, aggregate number of shares repurchased value     $ 65,400,000    
2016 Share Repurchase Program [Member] | Maximum [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Stock repurchase program, authorized amount         $ 200,000,000.0
2016 Share Repurchase Program [Member] | Common Class A [Member]          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Repurchase of common stock     18,200,000