CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net income (loss)	$ 44,319	$ (1,749)	$ 23,440
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	96,694	86,795	80,607
Amortization of operating lease right-of-use assets	73,967	67,915	66,842
Lease abandonment charges	19,675	0	0
Equity in earnings of joint ventures, net of dividends	(6,260)	1,577	248
Amortization and write off of deferred financing costs and loan discount	3,254	4,413	4,184
Loss on sale and disposal of equipment and other	1,246	1,200	2,383
Loss (gain) on extinguishment of debt	1,496	(4,047)	0
Gain on re-measurement of pre-existing interest	0	0	(768)
Loss on impairment	0	4,170	0
Amortization of cash flow hedge	3,695	3,448	0
Non-cash change in fair value of interest rate hedge	(21,670)	2,528	0
Stock-based compensation	25,203	12,405	8,730
Other non cash item in other expenses	0	242	(371)
Change in value of contingent consideration	0	0	(3,123)
Changes in operating assets and liabilities, net of assets acquired and liabilities assumed in purchase transactions:
Accounts receivable	(5,890)	25,206	(17,482)
Other current assets	(15,777)	6,588	(3,557)
Other assets	662	(5,425)	(2,326)
Deferred taxes	19,834	(611)	(3,888)
Operating lease liability	(72,553)	(53,906)	(66,831)
Deferred revenue	(28,319)	37,941	(1,082)
Accounts payable, accrued expenses and other liabilities	9,915	45,069	17,316
Net cash provided by operating activities	149,491	233,759	104,322
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of imaging facilities	(77,691)	(31,265)	(27,150)
Equity investments at fair value	0	0	(143)
Purchase of property and equipment	(137,874)	(94,172)	(74,153)
Purchase of intangible assets	(5,130)	0	0
Proceeds from sale of equipment	625	828	1,160
Proceeds from the sale of equity interests in a joint venture	0	0	132
Nulogix return of capital	0	0	792
Equity contributions in existing and purchase of interest in joint ventures	(1,441)	(1,635)	(103)
Net cash used in investing activities	(221,511)	(126,244)	(99,465)
CASH FLOWS FROM FINANCING ACTIVITIES
Principal payments on notes and leases payable	(3,302)	(3,562)	(6,494)
Payments on term loan debt	(619,529)	(43,296)	(40,742)
Additional deferred finance costs on revolving loan amendment	(938)	(741)	0
Proceeds from debt issuance, net of issuance costs	717,307	0	97,144
Proceeds from paycheck protection program loans	0	4,023	0
Distributions paid to noncontrolling interests	(2,426)	(1,985)	(3,057)
Proceeds from sale of economic interest in majority owned subsidiary	13,073	0	5,275
Contributions from noncontrolling partners	0	0	750
Proceeds from revolving credit facility	128,300	250,900	261,200
Payments on revolving credit facility	(128,300)	(250,900)	(289,200)
Proceeds from issuance of common stock upon exercise of options	488	0	75
Net cash provided by (used in) financing activities	104,673	(45,561)	24,951
EFFECT OF EXCHANGE RATE CHANGES ON CASH	(65)	(101)	(32)
NET INCREASE IN CASH AND CASH EQUIVALENTS	32,588	61,853	29,776
CASH AND CASH EQUIVALENTS, beginning of period	102,018	40,165	10,389
CASH AND CASH EQUIVALENTS, end of period	134,606	102,018	40,165
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid during the period for interest	29,042	39,521	46,254
Cash paid during the period for income taxes	$ 1,950	$ 5,069	$ 5,884