Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Voting Common Stock [Member] Common Stock [Member]	Non-voting Common Stock [Member] Common Stock [Member]	Paid-In Capital [Member]	Treasury Stock [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Loss [Member]	Total
Balance at Dec. 31, 2016	$ 216	$ 95	$ 1,019,988	$ (9,592)	$ (826,460)	$ (13,836)	$ 170,411
Balance, shares at Dec. 31, 2016	21,582	9,506		154
Net income (loss)					134,464
Other comprehensive income (loss)						(18,974)
Comprehensive income (loss)							115,490
Tax cuts and Jobs Act, reclassification tax effect					4,468	(4,468)
Cumulative effect adjustment attributable to previously unrecognized excess tax benefits on stock-based compensation					4,697		4,697
Balance at Dec. 31, 2017	$ 216	$ 95	1,019,988	$ (9,592)	(682,831)	(37,278)	290,598
Balance, shares at Dec. 31, 2017	21,582	9,506		154
Net income (loss)					4,294		4,294
Other comprehensive income (loss)						7,144	7,144
Comprehensive income (loss)							11,438
Cumulative effect adjustment attributable to investment in Telesat, net of tax of $5.4 million					(22,107)		(22,107)
Balance at Mar. 31, 2018	$ 216	$ 95	$ 1,019,988	$ (9,592)	$ (700,644)	$ (30,134)	$ 279,929
Balance, shares at Mar. 31, 2018	21,582	9,506		154