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Shareholders' Equity - Additional Information (Detail) - USD ($)
12 Months Ended
Jun. 10, 2017
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
May 16, 2017
Aug. 13, 2012
Class of Stock [Line Items]            
Issuance of common stock dividend reinvestment plan   100,000,000 100,000,000      
Number of stock option granted       128,000    
Share-based compensation expense   $ 2,700,000 $ 3,100,000 $ 1,700,000    
Tax benefit related to stock based compensation expense   $ 400,000 500,000 0    
Discount from market price   15.00%        
Employees offering dates intervals   6 months        
Number of shares authorized in employee stock purchase plan   1,500,000        
Employee stock purchase plan period   10 years        
Employee stock purchase plan number of shares remain available for future issuance   1,300,000        
Employee stock purchase plan expense   $ 60,000 90,000 $ 83,000    
Estimated weighted-average fair value of stock options granted       $ 2.68    
Expected volatility rate       39.00%    
Expected term period       6 years 3 months 18 days    
Risk-free interest rate       2.20%    
Expected dividend rate       3.30%    
Cash received from employee stock option exercised   7,000,000 100,000 $ 1,100,000    
Intrinsic value of option exercised   300 $ 24,000,000 $ 2,600,000    
Performance Units [Member]            
Class of Stock [Line Items]            
Maximum shares of common stock participant could receive upon vesting 77,778          
Common stock price threshold consecutive trading days 30 days          
Period to earn units based on stock price during thirty consecutive trading days 2 years          
Performance Units [Member] | Chief Executive Officer [Member]            
Class of Stock [Line Items]            
2017 stock options or stock awards, vesting period 3 years          
Number of stock awards granted 700,000          
Fair value of stock awards granted $ 175,000          
Restricted Stock and Performance Units [Member]            
Class of Stock [Line Items]            
Unrecognized compensation expense related to stock options and restricted stock   $ 6,400,000        
Weighted average vesting period   2 years 1 month 6 days        
Dividend Reinvestment Plan [Member]            
Class of Stock [Line Items]            
Issuance of common stock dividend reinvestment plan           750,000
2017 Plan [Member]            
Class of Stock [Line Items]            
Shares available for future grant   900,000        
2017 Plan [Member] | Common Stock [Member]            
Class of Stock [Line Items]            
Number of shares reserved for issuance         1,900,000  
2017 Plan [Member] | Minimum [Member]            
Class of Stock [Line Items]            
2017 stock options or stock awards, vesting period   3 years        
2017 Plan [Member] | Maximum [Member]            
Class of Stock [Line Items]            
2017 stock options or stock awards, vesting period   4 years        
2017 Plan [Member] | Employee Stock Option [Member]            
Class of Stock [Line Items]            
2017 stock options or stock awards, vesting period   4 years        
2007 Plan [Member]            
Class of Stock [Line Items]            
Number of stock option granted   0