Condensed Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	Voting Common Stock [Member] Common Stock [Member]	Nonvoting 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)					93,719		93,719
Other comprehensive income (loss)						(15,215)	(15,215)
Comprehensive income (loss)							78,504
Cumulative effect adjustment attributable to previously unrecognized excess tax benefits on stock-based compensation					4,741		4,741
Balance at Sep. 30, 2017	$ 216	$ 95	1,019,988	$ (9,592)	(728,000)	(29,051)	253,656
Balance, shares at Sep. 30, 2017	21,582	9,506		154
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
Other comprehensive income (loss)						(18,974)
Tax cuts and Jobs Act, reclassification tax effect						(4,468)
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
Balance at Sep. 30, 2017	$ 216	$ 95	1,019,988	$ (9,592)	(728,000)	(29,051)	253,656
Balance, shares at Sep. 30, 2017	21,582	9,506		154
Net income (loss)					40,745
Other comprehensive income (loss)						(3,759)
Comprehensive income (loss)							36,986
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					(44)		(44)
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)					50,935		50,935
Other comprehensive income (loss)						2,362	2,362
Comprehensive income (loss)							53,297
Cumulative effect adjustment attributable to investment in Telesat, net of tax of $5.9 million					(22,107)		(22,107)
Balance at Sep. 30, 2018	$ 216	$ 95	$ 1,019,988	$ (9,592)	$ (654,003)	$ (34,916)	$ 321,788
Balance, shares at Sep. 30, 2018	21,582	9,506		154