Acquisition (Preliminary Purchase Price Allocation) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Dec. 31, 2019	Jan. 02, 2019
Business Acquisition [Line Items]
Operating lease right-of-use assets		$ 80,805	$ 92,852
Operating lease liabilities		84,044	97,581
Goodwill		$ 137,728	$ 137,728
Quarton
Business Acquisition [Line Items]
Intangible assets				$ 22,200
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
Operating lease right-of-use assets				3,200
Intangible assets				22,200
Other assets				667
Compensation payable				637
Operating lease liabilities				3,200
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