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Employee Savings Plans - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Expenses related ESOP $ 7,849 $ 7,455 $ 10,789
Shares vested under ESOP 3,811,000    
Matching percentage of employer to employee contributions 100.00%    
Matching contributions to 401(k) retirement savings plan $ 15,456 14,178 $ 12,486
Temporary Equity, Shares Issued 105,931    
Deferred compensation $ 8,728 9,645  
Temporary Equity, Other Changes 8,993    
Temporary Equity, Accretion to Redemption Value, Adjustment $ (266)    
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]      
Assets, fair value disclosure $ 49,628 51,191  
Level 1 | Fair value, measurements, recurring      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Assets, fair value disclosure 49,330 48,238  
Level 1 | Fair value, measurements, recurring | Non-qualified deferred compensation assets      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Assets, fair value disclosure $ 49,330 $ 48,238