Nature of operations and summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2014

Accounting Policies [Abstract]

Components of Accounts Receivable

Accounts receivable consisted of the following at December 31:

	2014			2013
Joint interests	$	30,648		$	31,335
Accrued commodity sales	45,667			60,768
Derivative settlements	19,678			4,616
Production tax credits	2,031			694
Other	707			698
Allowance for doubtful accounts	(287		)	(1,596		)
	$	98,444		$	96,515

Components of Inventories

Inventories consisted of the following at December 31:

	2014			2013
Equipment inventory	$	24,169		$	13,657
Oil and natural gas inventory	2,575			3,186
Inventory valuation allowance	(1,187		)	(706		)
	$	25,557		$	16,137

Schedule Of Estimated Useful Lives for Property and Equipment

Estimated useful lives of our assets are as follows:

Furniture and fixtures			10 years
Automobiles and trucks			5 years
Machinery and equipment	10	—	20 years
Office and computer equipment	5	—	10 years
Building and improvements	10	—	40 years