Investment Securities and Equity Securities with Readily Determinable Fair Values (Unrealized and realized gains and losses recognized in net income on equity securities ) (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Investment Securities and Equity Securities with Readily Determinable Fair Values
Equity Securities	$ 6,013,000	$ 6,013,000	$ 27,885,000
Summary of unrealized and realized gains and losses recognized in net income on equity securities
Net losses recognized during the period on equity securities	(62,000)	(1,083,000)
Less: Net gains and (losses) recognized during the period on equity securities sold during the period	(771,000)	(771,000)
Unrealized gains (losses) recognized during the reporting period on equity securities still held at the reporting date	$ 709,000	$ (312,000)