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Earnings Per Share - Summary of Reconciliation of Numerators and Denominators Used in Basic and Diluted Per Share Computations (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Class A Common Stock [Member]    
Numerator:    
Allocation of net income $ 4,134 $ 9,487
Denominator:    
Weighted-average shares outstanding 21,545 20,545
Basic net income per share $ 0.19 $ 0.46
Numerator:    
Allocation of net income $ 4,134 $ 9,487
Denominator:    
Number of shares used in basic computation 21,545 20,545
Weighted-average shares effect of dilutive securities    
Add: Director and employee stock options 1,081 271
Number of shares used in diluted computation 22,626 20,816
Diluted net income per share $ 0.18 $ 0.46
Class B Common Stock [Member]    
Numerator:    
Allocation of net income $ 971 $ 2,362
Denominator:    
Weighted-average shares outstanding 5,577 5,577
Basic net income per share $ 0.17 $ 0.42
Numerator:    
Allocation of net income $ 971 $ 2,362
Denominator:    
Number of shares used in basic computation 5,577 5,577
Weighted-average shares effect of dilutive securities    
Number of shares used in diluted computation 5,577 5,577
Diluted net income per share $ 0.17 $ 0.42