Income taxes

The Company's tax provision for interim periods is determined using an estimate of its annual effective tax rate, adjusted for discrete items arising in that quarter. In each quarter, the Company updates its estimate of the annual effective tax rate, and if the estimated annual tax rate changes, a cumulative adjustment is made in that quarter.



	Three months ended						Nine months ended
(dollars in thousands)	September 30, 2016			September 30, 2015			September 30, 2016			September 30, 2015
Income tax expense (benefit)	$	(12,329	)	$	8,474		$	(43,562	)	$	22,975
Effective tax rate	10.6		%	31.1		%	12.6		%	24.6		%

The Company recorded an income tax benefit of $12.3 million for the three months ended September 30, 2016 due to a pre-tax net loss, which resulted in an effective tax rate of 10.6%. The lower effective tax rates for the three and nine months ended September 30, 2016 compared to 2015 resulted from the Company providing a net tax benefit on pre-tax losses in the United States, which was offset by income taxes paid at lower rates in profitable foreign jurisdictions (primarily Europe). The Company's provision for income taxes in each period has differed from the tax computed at U.S. federal statutory tax rates due to state taxes, the effect of non-U.S. operations, deductible and non-deductible stock-based compensation expense, federal research and development tax credits, and adjustments to unrecognized tax benefits.

The Company is currently under examination by the Internal Revenue Service for the 2012 through 2014 tax years and is unable to estimate the potential impact that the examination may have on income tax expense. If the examination is resolved unfavorably, there is a possibility it may have a material negative impact on the Company's results of operations.

At September 30, 2016 and December 31, 2015, the Company’s gross unrecognized tax benefits were $49.3 million and $36.3 million, respectively. If recognized, $31.2 million of these unrecognized tax benefits (net of U.S. federal benefit) at September 30, 2016 would be recorded as a reduction of future income tax provision. These unrecognized tax benefits relate primarily to unresolved matters with taxing authorities regarding the Company’s transfer pricing positions and tax positions based on the Company’s interpretation of certain U.S. trial and appellate court decisions, which remain subject to appeal and therefore could be overturned in future periods. The Company’s existing tax positions will continue to generate an increase in unrecognized tax benefits in subsequent periods. Management believes events that could occur in the next 12 months and cause a material change in unrecognized tax benefits include, but are not limited to, the completion of examinations by the U.S. or foreign taxing authorities and the expiration of statute of limitations on the Company's tax returns. Although the completion, settlement and closure of any audits is uncertain, it is reasonably possible that the total amount of unrecognized tax benefits will materially increase within the next 12 months. However, given the number of years remaining that are subject to examination, the range of the reasonably possible change cannot be estimated reliably.