Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating activities:
Net (loss) income	$ (73,328)	$ 19,321
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation	86,898	81,825
Loss (gain) on disposition of assets	4,287	(510)
Deferred tax provision	(7,769)	(49,089)
Stock-based compensation expense	1,414	1,597
Contract liabilities, net	11,980	(500)
Contract assets, net	(1,922)	611
Deferred contract costs, net	(6,244)	10,827
Other assets, noncurrent	98	228
Other liabilities, noncurrent	(570)	(1,811)
Other	(1,517)	3,182
Changes in operating assets and liabilities:
Accounts receivable	(20,761)	56,962
Prepaid expenses and other current assets	604	2,381
Accounts payable and accrued liabilities	13,329	(36,542)
Taxes payable	(3,637)	(4,713)
Net cash provided by operating activities	2,862	83,769
Investing activities:
Capital expenditures	(85,890)	(31,483)
Proceeds from maturities of marketable securities	1,000,000
Purchase of marketable securities	(948,298)
Proceeds from disposition of assets, net of disposal costs	95	1,427
Net cash used in investing activities	(34,093)	(30,056)
Financing activities:
Other	(2)	(66)
Net cash used in financing activities	(2)	(66)
Net change in cash and cash equivalents	(31,233)	53,647
Cash and cash equivalents, beginning of period	154,073	376,037
Cash and cash equivalents, end of period	$ 122,840	$ 429,684