Investment Securities - Unconsolidated Venture Capital and Private Equity Fund Investments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Investment	Dec. 31, 2017 USD ($) Investment
Upper Limit
Investment Holdings [Line Items]
Ownership interest percentage	5.00%	5.00%
Unconsolidated venture capital and private equity fund investments | Fair value accounting
Investment Holdings [Line Items]
Nonmarketable securities | $	$ 201,098	$ 98,548
Unconsolidated venture capital and private equity fund investments | Fair value accounting | Non-marketable securities
Investment Holdings [Line Items]
Number of investments | Investment	213	235