Accumulated Other Comprehensive Loss (Changes in Components of AOCI, Net of Related Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Balance, beginning	$ 995,338	$ 1,050,541	$ 1,009,855	$ 1,085,654
Other comprehensive (loss)/income, net of tax	(3,202)	4,628	(13,555)	16,588
Balance, ending	982,122	1,008,048	982,122	1,008,048
Accumulated Other Comprehensive Loss [Member]
Balance, beginning	(40,282)	(28,447)	(29,929)	(40,407)
Current period change, excluding amounts reclassified from accumulated other comprehensive loss	(5,315)	2,675	(19,222)	8,154
Amounts reclassified from accumulated other comprehensive loss	2,113	1,953	5,667	8,434
Other comprehensive (loss)/income, net of tax	(3,202)	4,628	(13,555)	16,588
Balance, ending	(43,484)	(23,819)	(43,484)	(23,819)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Balance, beginning	(31,901)	(18,420)	(21,520)	(28,989)
Current period change, excluding amounts reclassified from accumulated other comprehensive loss	(5,582)	2,548	(19,517)	8,315
Amounts reclassified from accumulated other comprehensive loss	2,113	1,953	5,667	6,755
Other comprehensive (loss)/income, net of tax	(3,469)	4,501	(13,850)	15,070
Balance, ending	(35,370)	(13,919)	(35,370)	(13,919)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance, beginning	(8,381)	(10,027)	(8,409)	(11,418)
Current period change, excluding amounts reclassified from accumulated other comprehensive loss	267	127	295	(161)
Amounts reclassified from accumulated other comprehensive loss				1,679
Other comprehensive (loss)/income, net of tax	267	127	295	1,518
Balance, ending	$ (8,114)	$ (9,900)	$ (8,114)	$ (9,900)