12.	INCOME TAXES

The provision for income taxes is based on a current estimate of the annual effective income tax rate adjusted to reflect the impact of discrete items. Significant management judgment is required in estimating operating income in order to determine our effective income tax rate. We recognized an income tax benefit of $5.3 million for the three months ended June 30, 2017, as compared to a $5.5 million tax expense for the three months ended June 30, 2016. Income tax expense decreased to $7.6 million for the six months ended June 30, 2017 from $15.4 million for the six months ended June 30, 2016. Our effective income tax rate was 16.1% and 34.6% for the six months ended June 30, 2017 and 2016, respectively. The lower effective income tax rate for the six months ended June 30, 2017 and the income tax benefit for the three months ended June 30, 2017 are primarily a result of the recognition of excess tax benefits from share-based payment awards vesting in the second quarter. We recognized a discrete adjustment to income tax expense for the three and six months ended June 30, 2017 in the amount of $8.2 million related to excess tax benefits.