Basis Of Presentation And Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment long-term debt	$ 309,702		$ 291,663
Adoption adjustment	301,835	$ 297,331	328,713	$ 296,556	$ 276,609	$ 285,696
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment	11,493	13,671	20,022	26,350	30,039	36,704
Additional Paid-In Capital [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adoption adjustment	305,157	$ 301,449	316,192	$ 293,022	$ 273,821	$ 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	(3,213)		3,200
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	$ (16,426)		$ 16,400