23. Income taxes

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.

As of December 31, 2016, the Company had unrecognized tax benefits amounting to $23,467, including an amount of $22,469, which, if recognized, would impact the effective tax rate.

The following table summarizes activities related to the Company’s unrecognized tax benefits for uncertain tax positions from January 1, 2017 to September 30, 2017:

	2017
Opening balance at January 1	$	23,467
Increase related to prior year tax positions, including recorded in acquisition accounting		515
Decrease related to prior year tax positions		(1,203	)
Decrease related to prior year tax positions due to lapse of applicable statute of limitation		(663	)
Effect of exchange rate changes		853
Closing balance at September 30	$	22,969

The Company’s unrecognized tax benefits as of September 30, 2017 include an amount of $21,964, which, if recognized, would impact the effective tax rate. As of December 31, 2016 and September 30, 2017, the Company had accrued approximately $3,856 and $4,266, respectively, for interest relating to unrecognized tax benefits. During the year ended December 31, 2016 and the nine months ended September 30, 2017, the company recognized approximately $(206) and 248, respectively, excluding the impact of exchange rate differences, in interest on unrecognized tax benefits. As of December 31, 2016 and September 30, 2017, the Company had accrued approximately $977 and $912, respectively, for penalties.