Accumulated Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	$ (54,914)
Other comprehensive income (loss), Net-of-tax Amount	31,290	$ (6,406)
Accumulated other comprehensive income (loss), ending balance	(23,624)		$ (54,914)	$ (54,914)
Pension and Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(16,167)	(14,656)		(14,656)
Other comprehensive income (loss) before reclassification				(2,307)
Amounts reclassified from accumulated other comprehensive income (loss)	239			796
Other comprehensive income (loss), Net-of-tax Amount	239			(1,511)
Accumulated other comprehensive income (loss), ending balance	(15,928)		(16,167)	(16,167)
Proportionate Share of Telesat Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(38,747)	(2,964)		(2,964)
Other comprehensive income (loss) before reclassification	31,051			(35,783)
Other comprehensive income (loss), Net-of-tax Amount	31,051			(35,783)
Accumulated other comprehensive income (loss), ending balance	(7,696)		(38,747)	(38,747)
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), beginning balance	(54,914)	(17,620)		(17,620)
Other comprehensive income (loss) before reclassification	31,051			(38,090)
Amounts reclassified from accumulated other comprehensive income (loss)	239			796
Other comprehensive income (loss), Net-of-tax Amount	31,290	$ (6,406)	(30,888)	(37,294)
Accumulated other comprehensive income (loss), ending balance	$ (23,624)		$ (54,914)	$ (54,914)