Other Current Assets

6 Months Ended

Jun. 30, 2020

Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]

Other Current Assets

Other Current Assets

The following table shows the breakdown in other current assets net book value for the presented periods:

	December 31, 2019		June 30, 2020
	(in thousands)
Prepayments to suppliers	$	5,109	$	5,671
Other debtors	4,225		2,809
Prepaid expenses	7,891		8,437
Derivative instruments	—		389
Gross book value at end of period	17,225		17,306
Net book value at end of period	$	17,225	$	17,306

Prepaid expenses mainly consist of office rental advance payments.

Derivative financial instruments include foreign currency swaps or forward purchases or sales contracts used to manage our exposure to the risk of exchange rate fluctuations. These instruments are considered level 2 financial instruments as they are measured using valuation techniques based on observable market data.