Composition of Certain Financial Statement Captions (Deferred Contract Costs) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Items Included in Consolidated Statement of Financial Condition [Abstract]
Deferred contract costs	$ 33,108,000		$ 33,108,000		$ 30,991,000
Capitalized contract cost, amount capitalized during period	$ 1,752,000	$ 1,950,000	4,749,000	$ 3,076,000
Amortization of deferred contract costs			2,632,000	$ 1,951,000
Capitalized contract cost impairment			$ 0