Investments (Gain (Loss) on Marketable Equity Securities) (Details 2) - USD ($) $ in Thousands	3 Months Ended							9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Investments [Abstract]
Gain on marketable equity securities, net	$ 17,404	$ 7,791	$ 24,066	$ (44,149)	$ 44,962	$ (2,554)	$ (14,102)	$ 49,261	$ 28,306	$ (15,843)	$ 0
Less: Net losses (gains) in earnings from marketable equity securities sold and donated	61				0			(2,919)	4,271
Net unrealized gains in earnings from marketable equity securities still held at the end of the period	$ 17,465				$ 44,962			$ 46,342	$ 32,577