Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of comprehensive income
Net income	$ 4,993	$ 9,902	$ 6,033	$ 5,128	$ 4,231	$ 4,554	$ 6,638	$ 4,262	$ 26,056	$ 19,685	$ 27,148
Mark to market of foreign exchange hedges									16	(128)	464
Deferred income tax (expense) benefit									(4)	29	(155)
Comprehensive (loss) income									$ 26,068	$ 19,586	$ 27,457