Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 897,482	$ 816,429	$ 859,947	$ 852,301
Other comprehensive income (loss) before reclassifications		(17,771)	810	(15,414)	(12,022)
Amounts reclassified from OCI		4	(42)	(341)	8
Ending balance		896,673	846,169	896,673	846,169
Accumulated Other Comprehensive (Loss) Income [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(163,543)	(162,116)	(165,555)	(149,334)
Ending balance		(181,310)	(161,348)	(181,310)	(161,348)
Cash Flow Hedges [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(58)	(34)	147	(669)
Other comprehensive income (loss) before reclassifications	[1]	(91)	(121)	(25)	404
Amounts reclassified from OCI	[1]	42	(12)	(229)	98
Ending balance	[1]	(107)	(167)	(107)	(167)
Pension Items [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	475	(369)	549	(309)
Other comprehensive income (loss) before reclassifications	[1]	0	0	0	0
Amounts reclassified from OCI	[1]	(38)	(30)	(112)	(90)
Ending balance	[1]	437	(399)	437	(399)
Foreign Currency Items [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(163,960)	(161,713)	(166,251)	(148,356)
Other comprehensive income (loss) before reclassifications		(17,680)	931	(15,389)	(12,426)
Amounts reclassified from OCI		0	0	0	0
Ending balance		$ (181,640)	$ (160,782)	$ (181,640)	$ (160,782)

[1] Cash Flow Hedges and Pension Items are net of tax.