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, 2018	Dec. 31, 2017
Investment Holdings [Line Items]
Nonmarketable securities	$ 118,333	$ 128,111
Strategic Investors Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	12,452	14,673
Capital Preferred Return Fund, LP
Investment Holdings [Line Items]
Nonmarketable securities	53,957	54,147
Growth Partners, LP
Investment Holdings [Line Items]
Nonmarketable securities	50,845	58,372
CP I, LP
Investment Holdings [Line Items]
Nonmarketable securities	$ 1,079	$ 919
Non-marketable securities | Strategic Investors Fund, LP
Investment Holdings [Line Items]
Ownership interest percentage	12.60%	12.60%
Non-marketable securities | Capital Preferred Return Fund, LP
Investment Holdings [Line Items]
Ownership interest percentage	20.00%	20.00%
Non-marketable securities | Growth Partners, LP
Investment Holdings [Line Items]
Ownership interest percentage	33.00%	33.00%
Non-marketable securities | CP I, LP
Investment Holdings [Line Items]
Ownership interest percentage	10.70%	10.70%