Composition of Certain Financial Statement Captions (Deferred Contract Costs) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Items Included in Consolidated Statement of Financial Condition [Abstract]
Deferred contract costs	$ 32,760,000		$ 30,991,000
Capitalized contract cost, amount capitalized during period	2,997,000	$ 1,126,000
Amortization of deferred contract costs	1,228,000	$ 988,000
Capitalized contract cost impairment	$ 0