9.INCOME TAXES

The components of our provision for income taxes are as follows:


	Three Months Ended
	March 31,
Income Tax Expense (Benefit) (in thousands):	2017			2016
Current tax benefit	$	(6)		$	—
Deferred tax expense (benefit)		78,312			(132,063)
	$	78,306		$	(132,063)
Combined federal and state effective income tax rate		37.4	%		36.3	%

At December 31, 2016, we had a U.S. net tax operating loss carryforward of approximately $1,182.4 million, which would expire in tax years 2031 through 2036. We believe that the carryforward will be utilized before it expires. We also had an alternative minimum tax credit carryforward of approximately $6.0 million.

At March 31, 2017, we had no unrecognized tax benefits that would impact our effective tax rate and have made no provisions for interest or penalties related to uncertain tax positions. The tax years 2013 through 2015 remain open to examination by the Internal Revenue Service of the United States. We file tax returns with various state taxing authorities, which remain open to examination for tax years 2012 through 2015.

Our combined federal and state effective income tax rates differ from the U.S. federal statutory rate of 35% primarily due to state income taxes and non-deductible expenses.