CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
CASH FLOWS FROM OPERATING ACTIVITIES
Net income (loss)	$ 30,337	$ 33,608	$ 44,319
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	128,391	115,877	96,694
Amortization of operating lease right-of-use assets	61,102	68,847	73,967
Lease abandonment charges	5,146	0	19,675
Equity in earnings of joint ventures, net of dividends	9,176	(5,952)	(6,260)
Amortization and write off of deferred financing costs and loan discount	2,987	2,693	3,254
Gain on contribution of imaging centers into joint venture	(16,808)	0	0
Loss on sale and disposal of equipment and other	2,187	2,529	1,246
Loss on extinguishment of debt	0	0	1,496
Loss on impairment	3,949	0	0
Amortization of cash flow hedge	3,576	3,687	3,695
Non-cash change in fair value of interest rate swap	8,185	(39,621)	(21,670)
Stock-based compensation	26,785	23,770	25,203
Change in value of contingent consideration	(3,880)	(325)	0
Changes in operating assets and liabilities, net of assets acquired and liabilities assumed in purchase transactions:
Accounts receivable	2,650	(30,078)	(5,890)
Other current assets	(8,441)	(3,327)	(15,777)
Other assets	(1,484)	(12,166)	662
Deferred taxes	6,056	13,356	19,834
Operating lease liability	(54,763)	(68,943)	(72,553)
Deferred revenue	626	(7,316)	(28,319)
Accounts payable, accrued expenses and other liabilities	15,086	49,778	9,915
Net cash provided by operating activities	220,863	146,417	149,491
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of imaging centers and other operations	(10,918)	(129,961)	(77,691)
Purchase of property and equipment	(176,600)	(119,451)	(137,874)
Purchase of intangible assets	0	0	(5,130)
Proceeds from sale of equipment	83	3,904	625
Equity contributions in existing and purchase of interest in joint ventures	(14,035)	(1,441)	(1,441)
Net cash used in investing activities	(201,470)	(246,949)	(221,511)
CASH FLOWS FROM FINANCING ACTIVITIES
Payments on term loan debt	(41,063)	(53,750)	(619,529)
Principal payments on notes and leases payable other than term loan debt	(2,930)	0	(3,302)
Additional deferred finance costs on revolving loan amendment	0	0	(938)
Proceeds from debt issuance, net of issuance costs	0	147,996	717,307
Distributions paid to noncontrolling interests	(5,972)	(893)	(2,426)
Proceeds from sale of economic interest in majority owned subsidiary	0	0	13,073
Proceeds from revolving credit facility	0	0	128,300
Payments on revolving credit facility	0	0	(128,300)
Sale of noncontrolling interests	5,121	0	0
Payments on contingent consideration	(5,495)	0	0
Proceeds from issuance of common stock, net of issuance costs	245,832	0	0
Proceeds from issuance of common stock upon exercise of options	142	294	488
Net cash provided by financing activities	195,635	93,647	104,673
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(292)	113	(65)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	214,736	(6,772)	32,588
CASH AND CASH EQUIVALENTS, beginning of period	127,834	134,606	102,018
CASH AND CASH EQUIVALENTS, end of period	342,570	127,834	134,606
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid during the period for interest	64,695	39,151	29,042
Cash paid during the period for income taxes	$ 1,587	$ 587	$ 1,950