Accumulated Other Comprehensive Loss (After-tax Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	$ 1,113,862		$ 998,286		$ 1,195,655	$ 876,764
Other comprehensive loss before reclassifications	(234)		(8,544)		(21,208)	(11,314)
Amounts reclassified from accumulated other comprehensive income (loss)	1,638		(171)		2,194	11,460
Net current-period other comprehensive income (loss)	1,404		(8,715)		(19,014)	146
Ending Balance	1,132,083		1,020,639		1,132,083	1,020,639
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(27,649)		2,474		(7,231)	(6,387)
Ending Balance	(26,245)		(6,241)		(26,245)	(6,241)
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(23,106)		(3,748)		(9,443)	(126)
Other comprehensive loss before reclassifications	(3,669)		(5,952)		(18,059)	(9,710)
Amounts reclassified from accumulated other comprehensive income (loss)	1,809		0		2,536	136
Net current-period other comprehensive income (loss)	(1,860)		(5,952)		(15,523)	(9,574)
Ending Balance	(24,966)		(9,700)		(24,966)	(9,700)
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	(5,574)		1,059		1,065	(11,550)
Other comprehensive loss before reclassifications	3,249		(2,035)		(3,390)	(1,092)
Amounts reclassified from accumulated other comprehensive income (loss)	0		0		0	11,666
Net current-period other comprehensive income (loss)	3,249		(2,035)		(3,390)	10,574
Ending Balance	(2,325)		(976)		(2,325)	(976)
Investment in Convertible Preferred Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	258		258		258	258
Other comprehensive loss before reclassifications	0	[1]	0	[1]	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	[1]	0		0	0
Net current-period other comprehensive income (loss)	0		0		0	0
Ending Balance	258		258		258	258
Defined Benefit Plan Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balance	773		4,905		889	5,031
Other comprehensive loss before reclassifications	186		(557)		241	(512)
Amounts reclassified from accumulated other comprehensive income (loss)	(171)		(171)		(342)	(342)
Net current-period other comprehensive income (loss)	15		(728)		(101)	(854)
Ending Balance	$ 788		$ 4,177		$ 788	$ 4,177

[1] All amounts are net of tax. Amounts in parentheses indicate debits