Summary of Significant Accounting Policies (Changes in AOCI Balances by Component) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Beginning balance	$ 1,553,856
Ending balance	1,654,921	$ 1,553,856
Accumulated Other Comprehensive Loss
Beginning balance	(46,741)	(42,100)	$ (45,449)
Other comprehensive income (loss) before reclassifications	1,330	(6,124)	2,026
Amounts reclassified from AOCI	1,776	1,483	1,323
Ending balance	(43,635)	(46,741)	(42,100)
Defined Benefit Pension Plan
Beginning balance	(44,087)	(37,826)	(38,670)
Other comprehensive income (loss) before reclassifications	4,167	(7,993)	(539)
Amounts reclassified from AOCI	2,054	1,732	1,383
Ending balance	(37,866)	(44,087)	(37,826)
Foreign Currency Translation
Beginning balance	(5,322)	(5,371)	(6,315)
Other comprehensive income (loss) before reclassifications	(465)	49	944
Amounts reclassified from AOCI	0	0	0
Ending balance	(5,787)	(5,322)	(5,371)
Unrealized Gain (Loss) in Fair Value of Investments
Beginning balance	2,668	1,097	(464)
Other comprehensive income (loss) before reclassifications	(2,372)	1,820	1,621
Amounts reclassified from AOCI	(278)	(249)	(60)
Ending balance	$ 18	$ 2,668	$ 1,097