Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities:
Net loss	$ (187,316)	$ (49,953)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation	175,151	163,650
Loss on impairment of assets		27,225
Gain on disposition of assets	(5,149)	(560)
Deferred tax provision	(31,125)	(61,160)
Stock-based compensation expense	2,956	2,468
Contract liabilities, net	14,017	(3,255)
Contract assets, net	(566)	(956)
Deferred contract costs, net	26,879	24,703
Other assets, noncurrent	(118)	742
Other liabilities, noncurrent	3	(3,849)
Other	(1,300)	2,577
Changes in operating assets and liabilities:
Accounts receivable	5,534	53,451
Prepaid expenses and other current assets	(2,002)	28
Accounts payable and accrued liabilities	9,961	(21,466)
Taxes payable	(9,608)	(2,878)
Net cash (used in) provided by operating activities	(2,683)	130,767
Investing activities:
Capital expenditures	(172,335)	(90,432)
Proceeds from maturities of marketable securities	2,025,000	300,000
Purchase of marketable securities	(1,872,107)	(573,837)
Proceeds from disposition of assets, net of disposal costs	15,573	1,723
Net cash used in investing activities	(3,869)	(362,546)
Financing activities:
Other	(12)	(90)
Net cash used in financing activities	(12)	(90)
Net change in cash and cash equivalents	(6,564)	(231,869)
Cash and cash equivalents, beginning of period	154,073	376,037
Cash and cash equivalents, end of period	$ 147,509	$ 144,168