Acquisition (Preliminary Purchase Price Allocation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Oct. 01, 2020	Jan. 02, 2019	Jan. 01, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Operating lease right-of-use assets	$ 78,241	$ 92,852			$ 103,700
Operating lease liabilities	(82,735)	(97,581)			$ (110,500)
Goodwill	147,084	137,728				$ 60,678
Quarton
Business Acquisition [Line Items]
Intangible assets				$ 22,200
Total estimated purchase price		103,000
MHT Partners [Member]
Business Acquisition [Line Items]
Intangible assets			$ 1,200
Total estimated purchase price	9,900
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
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, 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
Scenario, Plan | MHT Partners [Member]
Business Acquisition [Line Items]
Fixed assets			101
Operating lease right-of-use assets			1,120
Intangible assets			1,224
Other assets			43
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Compensation Payable			(533)
Operating lease liabilities			(1,446)
Total identifiable net assets acquired and liabilities assumed			509
Goodwill			$ 9,356
Total estimated purchase price	$ 9,865