Acquisition (Preliminary Purchase Price Allocation) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Jan. 02, 2019	Jan. 01, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Operating lease right-of-use assets	$ 96,664	$ 96,664		$ 103,694	$ 0
Operating lease liabilities	(100,934)	(100,934)		$ (110,505)	$ 0
Quarton
Business Acquisition [Line Items]
Operating lease right-of-use assets			$ 3,200
Intangible assets			22,200
Operating lease liabilities			(3,200)
Total estimated purchase price	$ 103,000
Scenario, Plan | Quarton
Business Acquisition [Line Items]
Cash and cash equivalents			12,236
Fees receivable			7,269
Fixed assets			1,085
Intangible assets			22,200
Other assets			667
Compensation payable			637
Due to related parties			4,750
Accounts payable, accrued expenses and other liabilities			16,257
Total identifiable net assets acquired and liabilities assumed			$ 21,813
Goodwill		81,150
Total estimated purchase price		$ 102,963