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Marketable Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Debt Securities, Available-for-sale [Line Items]
Proceeds from sale of common stock	$ 23,900
Recognized loss on sale of common stock included in interest and other income	5,000
Amortized Cost		$ 249,944
Unrealized Loss		(342)
Marketable securities	$ 0	$ 249,602
Cumulative Other Comprehensive Loss
Debt Securities, Available-for-sale [Line Items]
Reclassification pursuant to change in accounting principle			$ (1,902)
Retained Earnings
Debt Securities, Available-for-sale [Line Items]
Reclassification pursuant to change in accounting principle			1,902
Accounting Standards Update 2016-01 \| Cumulative Other Comprehensive Loss
Debt Securities, Available-for-sale [Line Items]
Reclassification pursuant to change in accounting principle			(1,900)
Accounting Standards Update 2016-01 \| Retained Earnings
Debt Securities, Available-for-sale [Line Items]
Reclassification pursuant to change in accounting principle			$ 1,900