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Stockholders' Equity - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
May 08, 2017
Dec. 31, 2016
Dec. 31, 2014
Stockholders Equity [Line Items]              
Common stock, shares issued 92,550,001   92,550,001     91,861,054  
Unvested shares of common stock 4,449,475   4,449,475        
Treasury stock, shares 6,519,773   6,519,773     6,519,773  
Dividends payable $ 505,000   $ 505,000     $ 908,000  
Dividends paid to stockholders     1,535,000 $ 56,756,000      
Share Repurchase Program, authorized amount             $ 250,000,000
Stock Purchase Agreement [Member] | ZHG Group [Member]              
Stockholders Equity [Line Items]              
Percentage of common stock outstanding         21.00%    
Stock Purchase Agreement [Member] | ZHG Group [Member] | Upon Closing of Sale [Member]              
Stockholders Equity [Line Items]              
Percentage of common stock outstanding         21.00%    
Acquisition price paid per share         $ 23.00    
Share Repurchase Program [Member]              
Stockholders Equity [Line Items]              
Share Repurchase Program, remaining authorized repurchase amount $ 190,000,000   $ 190,000,000        
Stock Repurchase Program, number of shares repurchased 0 0 0 0      
2.75x Modified Performance Restricted Shares [Member]              
Stockholders Equity [Line Items]              
Dividends paid to stockholders     $ 1,300,000