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Employee Savings Plans - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Expenses related ESOP $ 10,037 $ 8,241 $ 7,849
Shares vested under ESOP 3,315,000    
Matching percentage of employer to employee contributions 100.00%    
Matching contributions to 401(k) retirement savings plan $ 24,458 22,101 $ 15,456
Temporary equity, shares issued (in shares) 89,168    
Deferred compensation $ 6,837 11,717  
Temporary equity, other changes 7,346    
Temporary equity, accretion to redemption value, adjustment $ (509)    
Employee Stock Ownership Plan E S O P Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Maximum number of shares of common stock available for issuance 7,200,000    
Fair value, measurements, recurring      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Total assets at fair value $ 51,673 54,244  
Level 1 | Fair value, measurements, recurring      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Total assets at fair value 48,545 54,244  
Level 1 | Fair value, measurements, recurring | Non-qualified deferred compensation assets      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Total assets at fair value $ 48,545 $ 54,244  
Share-based Compensation Award, Tranche One      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
ESOP vesting period 2 years    
Share-based Compensation Award, Tranche Two      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
ESOP vesting period 3 years