v3.7.0.1
Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Balance Sheets (Detail) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Jun. 30, 2016
Dec. 31, 2015
Current Assets:        
Cash $ 2,323 $ 2,596 $ 8,567 $ 2,407
Short-term investments 237,433 289,806    
Accounts receivable - net 147,504 138,265    
Inventories of spare parts – net 76,155 70,402    
Prepaid expenses 13,131 9,259    
Deferred income taxes 10,798 10,798    
Income taxes receivable 414 540    
Total current assets 487,758 521,666    
Property and equipment – net 918,134 903,977    
Restricted cash and investments 12,396 13,038    
Other assets 10,172 9,759    
Total assets 1,428,460 1,448,440    
Current Liabilities:        
Accounts payable 27,791 28,704    
Accrued and other current liabilities 33,384 28,346    
Total current liabilities 61,175 57,050    
Long-term debt 631,096 631,247    
Deferred income taxes and other long-term liabilities 152,128 160,365    
Shareholders’ Equity:        
Common stock and paid-in capital 307,367 305,815    
Accumulated other comprehensive loss (254) (478)    
Retained earnings 276,948 294,441    
Total shareholders’ equity 584,061 599,778 625,346 626,998
Total liabilities and shareholders’ equity 1,428,460 1,448,440    
Eliminations [Member]        
Current Assets:        
Accounts receivable - net (2,819)      
Intercompany receivable (105,938) (57,904)    
Total current assets (108,757) (57,904)    
Investment in subsidiaries and others (376,032) (353,160)    
Total assets (484,789) (411,064)    
Current Liabilities:        
Accounts payable (2,819)      
Intercompany payable (105,938) (57,904)    
Total current liabilities (108,757) (57,904)    
Shareholders’ Equity:        
Common stock and paid-in capital (79,326) (79,191)    
Retained earnings (296,706) (273,969)    
Total shareholders’ equity (376,032) (353,160)    
Total liabilities and shareholders’ equity (484,789) (411,064)    
Parent Company Only (issuer) [Member]        
Current Assets:        
Cash 48 36 40 46
Short-term investments 237,433 289,806    
Accounts receivable - net 78,334 71,458    
Inventories of spare parts – net 67,148 61,834    
Prepaid expenses 10,554 6,990    
Deferred income taxes 10,798 10,798    
Income taxes receivable 418 558    
Total current assets 404,733 441,480    
Investment in subsidiaries and others 376,032 353,160    
Property and equipment – net 626,402 589,104    
Restricted cash and investments 12,382 13,023    
Other assets 9,168 8,660    
Total assets 1,428,717 1,405,427    
Current Liabilities:        
Accounts payable 24,177 22,744    
Accrued and other current liabilities 24,508 18,725    
Intercompany payable 97,739 57,904    
Total current liabilities 146,424 99,373    
Long-term debt 631,096 631,247    
Deferred income taxes and other long-term liabilities 67,136 75,029    
Shareholders’ Equity:        
Common stock and paid-in capital 307,367 305,815    
Accumulated other comprehensive loss (254) (478)    
Retained earnings 276,948 294,441    
Total shareholders’ equity 584,061 599,778    
Total liabilities and shareholders’ equity 1,428,717 1,405,427    
Guarantor Subsidiaries [Member]        
Current Assets:        
Cash 1,328 2,100 $ 8,527 $ 2,361
Accounts receivable - net 63,020 66,807    
Intercompany receivable 105,938 57,904    
Inventories of spare parts – net 9,007 8,568    
Prepaid expenses 2,394 2,269    
Income taxes receivable (4) (18)    
Total current assets 181,683 138,090    
Property and equipment – net 291,118 314,873    
Restricted cash and investments 0 15    
Other assets 1,004 1,099    
Total assets 473,805 454,077    
Current Liabilities:        
Accounts payable 3,200 5,960    
Accrued and other current liabilities 7,836 9,621    
Total current liabilities 11,036 15,581    
Deferred income taxes and other long-term liabilities 83,926 85,336    
Shareholders’ Equity:        
Common stock and paid-in capital 77,951 79,191    
Retained earnings 300,892 273,969    
Total shareholders’ equity 378,843 353,160    
Total liabilities and shareholders’ equity 473,805 454,077    
Non-Guarantor Subsidiaries [Member]        
Current Assets:        
Cash 947 460    
Accounts receivable - net 8,969      
Prepaid expenses 183      
Income taxes receivable 0      
Total current assets 10,099      
Property and equipment – net 614      
Restricted cash and investments 14      
Total assets 10,727      
Current Liabilities:        
Accounts payable 3,233      
Accrued and other current liabilities 1,040      
Intercompany payable 8,199      
Total current liabilities 12,472      
Deferred income taxes and other long-term liabilities 1,066      
Shareholders’ Equity:        
Common stock and paid-in capital 1,375      
Retained earnings (4,186)      
Total shareholders’ equity (2,811)      
Total liabilities and shareholders’ equity $ 10,727      
Guarantor and Non-Guarantor Subsidiaries [Member]        
Current Assets:        
Cash   $ 2,560