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Stock and Stock-based Compensation - Additional Information (Detail) - USD ($)
$ in Thousands
1 Months Ended 12 Months Ended
Feb. 28, 2017
Dec. 31, 2017
Dec. 31, 2016
May 31, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Common stock issued in connection with ESPP   7,151 8,142  
Additional compensation cost that will be recognized in future periods   $ 560    
Director        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock units reserved for issuance in lieu of retainer fee   72,000 73,750  
Minimum | Director        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Percentage of retainer fee to acquire common stock   50.00%    
Maximum | Director        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Percentage of retainer fee to acquire common stock   100.00%    
Restricted Stock Units (RSUs)        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Conversion of stock RSU to Common, ratio   100.00%    
Convert to common stock   25.00%    
Increment period for awards converted into common stock   4 years    
Stock compensation expense   $ 300 $ 490  
Weighted average period additional compensation cost will be expensed   3 years    
Vesting percentage     75.00%  
Granted restricted stock unit 605,000 56,759 31,327  
Restricted Stock Units (RSUs) | Award Subject to 2018 Performance Measures        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Granted restricted stock unit 541,000      
Restricted Stock Units (RSUs) | Two Thousand Seven Employee Stock Incentive Plan        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Shares available for issuance under the plan       1,700,000
Board of Directors Deferred Compensation | Director | General and Administrative Expense        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock compensation expense   $ 80 $ 70  
Common Stock        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Shares issued during period   351,024 113,579  
Common stock issued as payment of accrued preferred dividends   246,803    
Common stock issued upon the vesting of restricted stock units [1]   97,070 105,437  
Common stock issued in connection with ESPP   7,151 8,142  
[1] Converted to common stock.