v3.5.0.2
Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Balance Sheets (Detail) - USD ($)
$ in Thousands
Sep. 30, 2016
Dec. 31, 2015
Sep. 30, 2015
Dec. 31, 2014
Current Assets:        
Cash $ 2,639 $ 2,407 $ 5,552 $ 6,270
Short-term investments 289,520 284,523    
Accounts receivable - net 142,475 144,778    
Inventories of spare parts - net 69,409 69,491    
Prepaid expenses 6,976 8,951    
Deferred income taxes 10,379 10,379    
Income taxes receivable 863 761    
Total current assets 522,261 521,290    
Property and equipment - net 916,560 883,529    
Restricted cash and investments 13,038 15,336    
Other assets 7,334 6,178    
Total assets 1,459,193 1,426,333    
Current Liabilities:        
Accounts payable 20,843 31,373    
Accrued and other current liabilities 32,178 44,759    
Total current liabilities 53,021 76,132    
Long-term debt:        
Revolving credit facility 132,400 57,500    
Senior Notes dated March 17, 2014, net of debt issuance costs of $3,064 496,936 496,001    
Deferred income taxes and other long-term liabilities 155,349 169,702    
Shareholders' Equity:        
Common stock and paid-in capital 310,259 306,444    
Accumulated other comprehensive income (loss) (271) (567)    
Retained earnings 311,499 321,121    
Total shareholders' equity 621,487 626,998 624,195 597,068
Total liabilities and shareholders' equity 1,459,193 1,426,333    
Parent Company Only (issuer) [Member]        
Current Assets:        
Cash 36 46 1,460 51
Short-term investments 289,520 284,523    
Accounts receivable - net 64,564 70,336    
Inventories of spare parts - net 60,416 60,060    
Prepaid expenses 4,412 7,162    
Deferred income taxes 10,379 10,379    
Income taxes receivable 950 1,002    
Total current assets 430,277 433,508    
Investment in subsidiaries 351,440 330,848    
Property and equipment - net 602,296 632,759    
Restricted cash and investments 13,023 15,336    
Other assets 6,181 5,975    
Total assets 1,403,217 1,418,426    
Current Liabilities:        
Accounts payable 17,232 25,512    
Accrued and other current liabilities 21,894 29,138    
Intercompany payable 41,796 90,943    
Total current liabilities 80,922 145,593    
Long-term debt:        
Revolving credit facility 132,400 57,500    
Senior Notes dated March 17, 2014, net of debt issuance costs of $3,064 496,936 496,001    
Deferred income taxes and other long-term liabilities 71,472 92,334    
Shareholders' Equity:        
Common stock and paid-in capital 310,259 306,444    
Accumulated other comprehensive income (loss) (271) (567)    
Retained earnings 311,499 321,121    
Total shareholders' equity 621,487 626,998    
Total liabilities and shareholders' equity 1,403,217 1,418,426    
Guarantor Subsidiaries [Member]        
Current Assets:        
Cash [1] 2,603 2,361 $ 4,092 $ 6,219
Accounts receivable - net [1] 77,911 74,442    
Intercompany receivable [1] 41,796 90,943    
Inventories of spare parts - net [1] 8,993 9,431    
Prepaid expenses [1] 2,564 1,789    
Income taxes receivable [1] (87) (241)    
Total current assets [1] 133,780 178,725    
Property and equipment - net [1] 314,264 250,770    
Restricted cash and investments [1] 15      
Other assets [1] 1,153 203    
Total assets [1] 449,212 429,698    
Current Liabilities:        
Accounts payable [1] 3,611 5,861    
Accrued and other current liabilities [1] 10,284 15,621    
Total current liabilities [1] 13,895 21,482    
Long-term debt:        
Deferred income taxes and other long-term liabilities [1] 83,877 77,368    
Shareholders' Equity:        
Common stock and paid-in capital [1] 79,191 79,061    
Retained earnings [1] 272,249 251,787    
Total shareholders' equity [1] 351,440 330,848    
Total liabilities and shareholders' equity [1] 449,212 429,698    
Eliminations [Member]        
Current Assets:        
Intercompany receivable (41,796) (90,943)    
Total current assets (41,796) (90,943)    
Investment in subsidiaries (351,440) (330,848)    
Total assets (393,236) (421,791)    
Current Liabilities:        
Intercompany payable (41,796) (90,943)    
Total current liabilities (41,796) (90,943)    
Shareholders' Equity:        
Common stock and paid-in capital (79,191) (79,061)    
Retained earnings (272,249) (251,787)    
Total shareholders' equity (351,440) (330,848)    
Total liabilities and shareholders' equity $ (393,236) $ (421,791)    
[1] Foreign subsidiaries represent minor subsidiaries and are included in the guarantor subsidiaries' amounts.