Investments - Narrative (Details) - USD ($)	9 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Investments [Abstract]
Short-term investments	$ 4,000,000		$ 1,295,300,000
Adjusted Cost			1,292,500,000
Marketable equity securities	1,700,000		2,800,000
Sales of available-for-sale investments	1,376,600,000	$ 0
Available-for-sale securities, recognized losses	5,600,000
Loss on marketable equity securities	$ 1,200,000
Other than temporary impairment losses, available-for-sale securities			$ 15,500,000