Fair Value Measurements - Unobservable Inputs Reconciliation - Assets (Details) - Fair Value, Measurements, Recurring - Level 3 - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 74,377	$ 61,917
Purchases	126	14,943
Sales and cash collections	(4,180)	(3,846)
Realized gains	2,980	2,886
Unrealized gains	460	3,774
Unrealized losses	(19,795)
Balance at end of period	53,968	79,674
Investments in Associated Companies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	52,240	40,643
Purchases	0	14,943
Sales and cash collections	0	0
Realized gains	0	0
Unrealized gains	460	3,774
Unrealized losses	(19,795)
Balance at end of period	32,905	59,360
Marketable Securities and Other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	22,137	21,274
Purchases	126	0
Sales and cash collections	(4,180)	(3,846)
Realized gains	2,980	2,886
Unrealized gains	0	0
Unrealized losses	0
Balance at end of period	$ 21,063	$ 20,314