Basis Of Presentation And Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Jan. 01, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment long-term debt	$ 309,405			$ 291,663
Adoption adjustment	311,541	$ 301,835		328,713	$ 325,766	$ 296,556	$ 285,696
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment	22,075	11,493		20,022	23,480	26,350	36,704
Additional Paid-In Capital [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment	$ 309,290	$ 305,157		316,192	$ 316,394	$ 293,022	$ 271,782
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2020-06 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment long-term debt			$ 20,400
Adoption adjustment				(19,639)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2020-06 [Member] | Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment			3,200	(3,213)
Cumulative Effect, Period of Adoption, Adjustment [Member] | Accounting Standards Update 2020-06 [Member] | Additional Paid-In Capital [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment			$ 16,400	$ (16,426)