Investments In Securities Investments in Securities (Schedule of Carrying Value and Fair Value of Financial Assets Disclosed) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	$ 43,992	$ 18,694
Accrued interest and dividends	1,161	946
Equity Securities, Estimated Fair Value	55,785	48,489
Commercial paper and money market funds	21,714	32,787
Equity investments in unconsolidated affiliates, equity method	5,629	5,847
Equity investments in unconsolidated affiliates, measurement alternative	7,060	6,589	$ 5,439
Assets, fair value disclosure	135,341	113,352
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	43,992	18,694
Accrued interest and dividends	1,161	946
Equity Securities, Estimated Fair Value	55,785	48,489
Commercial paper and money market funds	21,714	32,787
Equity investments in unconsolidated affiliates, equity method	0	0
Equity investments in unconsolidated affiliates, measurement alternative	0	0
Assets, fair value disclosure	122,652	100,916
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Accrued interest and dividends	0	0
Equity Securities, Estimated Fair Value	0	0
Commercial paper and money market funds	0	0
Equity investments in unconsolidated affiliates, equity method	0	0
Equity investments in unconsolidated affiliates, measurement alternative	0	0
Assets, fair value disclosure	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Accrued interest and dividends	0	0
Equity Securities, Estimated Fair Value	0	0
Commercial paper and money market funds	0	0
Equity investments in unconsolidated affiliates, equity method	5,629	5,847
Equity investments in unconsolidated affiliates, measurement alternative	7,060	6,589
Assets, fair value disclosure	$ 12,689	$ 12,436