SCHEDULE II- VALUATION AND QUALIFYING ACCOUNTS - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
allowance for uncollectible notes [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance, January 1		$ 0
Charged to Cost and Expense		44,038
Deductions	[1]	0
Ending Balance, December 31		44,038	$ 0
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance, January 1		2,009	486	$ 896
Charged to Cost and Expense		1,309	1,700	78
Deductions	[1]	1,128	177	488
Ending Balance, December 31		2,190	2,009	486
Valuation Allowance for Unproved Natural Gas and Crude Oil Properties [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance, January 1		144	9,293	5,142
Charged to Cost and Expense		215	7,012	4,465
Deductions	[1]	0	16,161	314
Ending Balance, December 31		$ 359	$ 144	$ 9,293

[1] For allowance for doubtful accounts, deductions represent the write-off of accounts receivable deemed uncollectible. For allowance for expirations of unproved crude oil and natural gas properties, deductions represent accumulated amortization of expired or abandoned unproved crude oil and natural gas properties, with a corresponding decrease to the historical cost of the associated asset.