INCOME TAXES

Our effective tax rate is impacted primarily by the amount of taxable income associated with each jurisdiction in which our income is subject to income tax, permanent differences between the financial statement carrying amounts and tax bases of assets and liabilities.

During the three-month periods ended March 31, 2017, and 2016, our effective tax rate was 0% which differed from the statutory rate primarily as a result of the impact of recording a valuation allowance to offset the amount of additional deferred tax asset generated during the periods.

As of March 31, 2017, we do not believe it is more likely than not that we will fully realize the benefit of our deferred tax assets. As such, we increased the valuation allowance related to our deferred tax assets by $4.4 million for the three months ended March 31, 2017. We recognized a full valuation allowance against our net deferred tax assets as of March 31, 2017, and December 31, 2016.

A summary of our valuation allowance activity is as follows (in thousands):



	Three Months Ended March 31,
	2017		2016
Valuation allowance, beginning of period	$	326,097	$	300,601
Additions	4,425		8,004
Valuation allowance, end of period	$	330,522	$	308,605