Comprehensive Income (Changes in Accumulated Other Comprehensive Loss by Component) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (93,596)	$ 508,022	$ 837,656	$ 551,519
Other comprehensive income (loss) before reclassifications			(241)
Amounts reclassified from accumulated other comprehensive loss			1,041
Other comprehensive income (loss)	2,138	(1,872)	800	1,672
Ending balance	68,800	712,911	68,800	712,911
Foreign Currency [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(2,946)
Other comprehensive income (loss) before reclassifications			0
Amounts reclassified from accumulated other comprehensive loss			0
Other comprehensive income (loss)			0
Ending balance	(2,946)		(2,946)
Unrealized Net (Loss) Gains on Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(139)
Other comprehensive income (loss) before reclassifications			145
Amounts reclassified from accumulated other comprehensive loss			(20)
Other comprehensive income (loss)			125
Ending balance	(14)		(14)
Unrealized Gain on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			868
Other comprehensive income (loss) before reclassifications			(394)
Amounts reclassified from accumulated other comprehensive loss			1,061
Other comprehensive income (loss)			667
Ending balance	1,535		1,535
Other Comprehensive Loss on Pension Liability [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance			(2,910)
Other comprehensive income (loss) before reclassifications			8
Amounts reclassified from accumulated other comprehensive loss			0
Other comprehensive income (loss)			8
Ending balance	(2,902)		(2,902)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(6,465)	(4,610)	(5,127)	(8,154)
Other comprehensive income (loss)	2,138	(1,872)	800	1,672
Ending balance	$ (4,327)	$ (6,482)	$ (4,327)	$ (6,482)