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Supplemental Information to Consolidated Statements of Cash Flows - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Jun. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Cash Flow Supplemental Disclosures [Line Items]            
Restricted stock surrendered, in values           $ 1,000
Common Stock            
Cash Flow Supplemental Disclosures [Line Items]            
Restricted stock surrendered, (in shares)       9,000 25,000 52,000
Restricted stock surrendered, in values           $ 1,000
Common Stock | 4.25% Convertible Senior Notes (due 2018)            
Cash Flow Supplemental Disclosures [Line Items]            
Common stock shares issued upon conversion of debt instrument 112,400 112,400 2,865,000 3,000,000    
Common stock shares issued upon conversion of debt instrument, value $ 400,000   $ 15,100,000 $ 15,500,000    
Restricted Stock            
Cash Flow Supplemental Disclosures [Line Items]            
Restricted stock surrendered, (in shares)       29,689 50,719 52,024
Restricted stock surrendered, in values       $ 79,000 $ 1,500,000 $ 400,000
Tax benefit (deficiency) related to restricted stock compensation       $ 0 $ 500,000  
Employees - including an executive officer            
Cash Flow Supplemental Disclosures [Line Items]            
Restricted stock surrendered, (in shares)       29,689 50,719 52,024
Restricted stock surrendered, in values         $ 1,500,000 $ 400,000
Employees - including an executive officer | Maximum            
Cash Flow Supplemental Disclosures [Line Items]            
Restricted stock surrendered, in values       $ 100,000