Investment Securities - Consolidated Venture Capital and Private Equity Fund Investments (Details) - Consolidated venture capital and private equity fund investments - Fair value accounting - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Nonmarketable securities	$ 87,180	$ 118,333
Strategic Investors Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 5,729	$ 12,452
Strategic Investors Fund, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	12.60%	12.60%
Capital Preferred Return Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 45,341	$ 53,957
Capital Preferred Return Fund, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	20.00%	20.00%
Growth Partners, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 35,976	$ 50,845
Growth Partners, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	33.00%	33.00%
CP I, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 134	$ 1,079
CP I, LP | Non-marketable securities
Investment Holdings [Line Items]
Ownership interest percentage	10.70%	10.70%