Investments in Affiliates (Equity Method Investment, Summarized Financial Data) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Assets:
Current assets	$ 28,489		$ 34,091
Total assets	281,944		254,469
Liabilities and Shareholder's Equity:
Current liabilities	3,559		4,841
Total liabilities	43,511		44,936
Stockholder's Equity	238,433	$ 259,974	209,533	$ 350,027
Statement of Operations Data:
Operating income (loss)	(1,729)	(1,648)
Interest expense	(6)	(5)
Income tax (provision) benefit	222	(2,116)
Telesat Canada [Member]
Assets:
Current assets	759,747		703,210
Total assets	4,018,684		3,943,875
Liabilities and Shareholder's Equity:
Current liabilities	157,117		129,849
Long-term debt	2,483,716		2,483,256
Total liabilities	3,158,126		3,140,747
Stockholder's Equity	860,558		$ 803,128
Statement of Operations Data:
Revenues	150,054	158,565
Operating expenses	(31,540)	(35,316)
Depreciation and amortization	(42,713)	(45,417)
Other operating income (expense)	(495)	(167)
Operating income (loss)	75,306	77,665
Interest expense	(33,100)	(41,547)
Foreign exchange gain (loss)	27,427	(221,643)
Gain (loss) on financial instruments	1,585	(7,005)
Other income (expense)	(797)	3,539
Income tax (provision) benefit	(16,910)	682
Net income (loss)	$ 53,511	$ (188,309)