Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]
Cash paid for interest, expensed		$ 72,842	$ 50,076	$ 98,261
Cash paid for interest, capitalized		36,671	37,079	30,762
Cash paid for interest, treated as a reduction of debt		85,303	79,606	50,349
Cash paid for income taxes		2,361	492	450
Cash received from income tax refunds		9,820	8,280	13,323
Noncash investing and financing activities
Increase in asset retirement obligations		13,560	4,499	9,565
Increase (decrease) in liabilities for capital expenditures		(17,740)	14,600	3,930
Conversion of convertible senior notes into common stock	$ 162,000	0	162,004	0
Treasury Stock
Other Significant Noncash Transactions [Line Items]
Retirement of treasury stock		$ 0	$ 0	$ 46,562