CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 209,627	$ 113,346
Accounts receivable, net of allowance for doubtful accounts of $3,191 and $3,545 at June 30, 2016 and December 31, 2015, respectively	128,551	219,672
Federal and state income taxes receivable	36,671	33,454
Inventory	11,532	14,716
Deferred tax assets, net	28,487	65,121
Other	40,855	40,227
Total current assets	455,723	486,536
Property and equipment, net	3,640,894	3,920,708
Goodwill and intangible assets	90,788	92,609
Deposits on equipment purchases	17,970	22,367
Other	6,096	7,264
Total assets	4,211,471	4,529,484
Current liabilities:
Accounts payable	66,343	82,771
Accrued expenses	139,922	161,611
Current portion of long-term debt, net of debt issuance cost of $529 and $483 at June 30, 2016 and December 31, 2015, respectively	85,721	63,267
Total current liabilities	291,986	307,649
Long-term debt, net of debt issuance cost of $2,581 and $3,350 at June 30, 2016 and December 31, 2015, respectively	741,169	787,900
Deferred tax liabilities, net	768,556	863,833
Other	7,930	8,971
Total liabilities	1,809,641	1,968,353
Commitments and contingencies (see Note 9)
Stockholders' equity:
Preferred stock, par value $.01; authorized 1,000,000 shares, no shares issued
Common stock, par value $.01; authorized 300,000,000 shares with 191,112,033 and 190,374,801 issued and 147,735,741 and 147,167,561 outstanding at June 30, 2016 and December 31, 2015, respectively	1,911	1,904
Additional paid-in capital	1,023,001	1,011,811
Retained earnings	2,284,520	2,458,554
Accumulated other comprehensive income (loss)	3,054	(4,093)
Treasury stock, at cost, 43,376,292 and 43,207,240 shares at June 30, 2016 and December 31, 2015, respectively	(910,656)	(907,045)
Total stockholders' equity	2,401,830	2,561,131
Total liabilities and stockholders' equity	$ 4,211,471	$ 4,529,484

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.