General - Schedule of Major Streams of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Revenue from contracts with customers	$ 104,299	$ 98,443	$ 183,227	$ 174,312
Alternative revenue programs, net - WCMA	(327)	3,933	(2,306)	3,601
Other balancing and memorandum accounts revenue, net	(2,376)	(4,611)	(3,009)	(6,447)
Rental income	1,369	1,321	2,735	2,662
Total revenues	$ 102,965	$ 99,086	$ 180,647	$ 174,128