The Company determines its tax provision for interim periods using an estimate of its annual effective tax rate adjusted for discrete items, if any, that are taken into account in the relevant period. Each quarter, the Company updates its estimate of the annual effective tax rate, and if its estimated tax rate changes, the Company makes a cumulative adjustment.

The Company’s effective tax rate (“ETR”) was 22.8% for the six months ended June 30, 2019, up from 18.4% for the six months ended June 30, 2018. The increase in the Company’s effective tax rate is primarily due to the expiration of certain special economic zone benefits in India, tax costs relating to an internal restructuring, changes in the jurisdictional mix of the Company’s income, as well as certain tax benefits recorded in the six months ended June 30, 2018.

As of December 31, 2018, the Company had unrecognized tax benefits amounting to $26,722, including an amount of $25,485, which, if recognized, would impact the Company’s ETR.

The following table summarizes activities related to the Company’s unrecognized tax benefits for uncertain tax positions for six months ended June 30, 2019:

	2019
Opening balance at January 1	$	26,722
Decrease related to prior year tax positions		(56	)
Decrease related to prior year tax position due to lapse of applicable statute of limitation		(66	)
Increase related to current year tax positions, including recorded in acquisition accounting		150
Effect of exchange rate changes		337
Closing balance at June 30	$	27,087

The Company’s unrecognized tax benefits as of June 30, 2019 include an amount of $25,850, which, if recognized, would impact the Company’s ETR. As of December 31, 2018 and June 30, 2019 the Company had accrued approximately $5,081 and $5,525, respectively, in interest relating to unrecognized tax benefits. During the year ended December 31, 2018 and the six months ended June 30, 2019, the Company recognized approximately $467 and $444, respectively, excluding the impact of exchange rate differences, in interest on unrecognized tax benefits. As of December 31, 2018 and June 30, 2019, the Company had accrued approximately $995 and $922, respectively, for penalties.