Stockholders' Equity (Schedule of Changes in Accumulated Other Comprehensive Income (Loss) by Component) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Estimated tax benefit (provision)
Beginning balance	$ 1,000	$ 11,000	$ 133,000
Other comprehensive income (loss) before reclassifications	174,000	(332,000)	(249,000)
Less: Amount reclassified from accumulated other comprehensive income (loss)	166,000	(322,000)	(123,000)
Net current period other comprehensive income (loss)	8,000	(10,000)	(126,000)
Distribution of Arlo			4,000
Ending balance	9,000	1,000	11,000
AOCI, after tax
Beginning balance	608,693,000	627,552,000	730,485,000
Other comprehensive income (loss) before reclassifications	(682,000)	1,249,000	1,301,000
Less: Amount reclassified from accumulated other comprehensive income (loss)	(626,000)	1,213,000	465,000
Net current period other comprehensive income (loss)	(56,000)	36,000	836,000
Distribution of Arlo			0
Ending balance	689,384,000	608,693,000	627,552,000
Unrealized gains (losses) on available-for-sale investments
AOCI, before tax
Beginning balance	(2,000)	(18,000)	(146,000)
Other comprehensive income (loss) before reclassifications	0	16,000	128,000
Less: Amount reclassified from accumulated other comprehensive income (loss)	0	0	0
Net current period other comprehensive income (loss)	0	16,000	128,000
Distribution of Arlo			0
Ending balance	(2,000)	(2,000)	(18,000)
Unrealized gains (losses) on derivatives
AOCI, before tax
Beginning balance	22,000	(8,000)	(838,000)
Other comprehensive income (loss) before reclassifications	(856,000)	1,565,000	1,422,000
Less: Amount reclassified from accumulated other comprehensive income (loss)	(792,000)	1,535,000	588,000
Net current period other comprehensive income (loss)	(64,000)	30,000	834,000
Distribution of Arlo			(4,000)
Ending balance	(42,000)	22,000	(8,000)
AOCI
AOCI, after tax
Beginning balance	21,000	(15,000)	(851,000)
Ending balance	$ (35,000)	$ 21,000	$ (15,000)