Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Oct. 01, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018
Accounting Policies [Abstract]
Cash and cash equivalents		$ 396,219				$ 220,370
Restricted cash and cash equivalents		$ 58,000				33,300
Restricted cash and cash equivalents, balance sheet location		us-gaap:OtherAssets
Right-of-use asset, amount		$ 15,500			$ 15,700
Lease liability, amount		15,511			$ 15,500
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment		1,300,520	$ 1,287,793	$ 1,306,594		1,336,326	$ 1,327,099	$ 1,355,983	$ 1,345,913	$ 1,391,622
ACL		$ 31,215	$ 31,196			9,226	$ 9,036	$ 8,619		8,463
Minimum [Member] | Forecast [Member] | Accounting Standards Update 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
ACL	$ 20,000
Maximum [Member] | Forecast [Member] | Accounting Standards Update 2016-13 [Member]
Summary Of Significant Accounting Policies [Line Items]
ACL	$ 32,000
Cumulative effect of adopting ASU [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment						$ 88				$ 394