Summary of Critical and Significant Accounting Policies - Marketable Securities (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Marketable Securities [Line Items]
Carrying Value		$ 2,500	$ 3,600
Equity securities:
Gross Unrealized Gain		12,515	5,710	$ (5,159)
Carrying Value		2,500	3,600
Held to maturity:
Total - Marketable securities, amortized cost		131,770	140,649
Total - Marketable securities, gross unrealized gain (loss)		15,998	3,544
Total - Marketable securities, carrying value		147,768	144,193
Marketable securities, allowance for credit loss		0	0
Proceeds from maturity of mortgage backed security	$ 83,100	91,700	83,100
Accelerated interest income		11,800	7,000
Proceeds from sale and maturities of marketable securities		113,500	147,500	31,500
Marketable securities, realized gain (loss)		2,100	1,300	700
Unrealized gain (loss) on equity securities recognized through income		12,515	5,710	$ (5,159)
Interest and Other Income
Equity securities:
Gross Unrealized Gain		12,500	5,700
Held to maturity:
Unrealized gain (loss) on equity securities recognized through income		12,500	5,700
Investment Funds - Debt Securities
Marketable Securities [Line Items]
Carrying Value		50,631	30,132
Equity securities:
Amortized Cost		49,646	29,588
Gross Unrealized Gain		985	544
Carrying Value		50,631	30,132
Held to maturity:
Unrealized gain (loss) on equity securities recognized through income		985	544
Common Stock and Stock Funds
Marketable Securities [Line Items]
Carrying Value		96,075	37,868
Equity securities:
Amortized Cost		81,074	34,941
Gross Unrealized Gain		15,001	2,927
Carrying Value		96,075	37,868
Held to maturity:
Unrealized gain (loss) on equity securities recognized through income		15,001	2,927
U.S. Treasury Securities
Available for sale
Available-for-sale, amortized cost			2,421
Available-for-sale, gross unrealized gain (Loss)			13
Available-for-sale, carrying value			2,434
Investment-Grade Unsecured Debt
Available for sale
Available-for-sale, amortized cost		1,050	1,048
Available-for-sale, gross unrealized gain (Loss)		12	60
Available-for-sale, carrying value		1,062	1,108
Allowance for Credit Losses		0
Mortgage Backed Securities
Held to maturity:
Held to maturity, amortized cost			72,651
Held to maturity, gross unrealized gain (loss)			0
Held to maturity carrying value		$ 0	$ 72,651