CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (13,998)	$ (1,922)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	21,934	19,620
Amortization of operating lease right-of-use assets	17,259	16,000
Equity in earnings of joint ventures	(1,955)	(1,873)
Amortization of deferred financing costs and loan discount	1,081	975
Loss on sale and disposal of equipment and other	771	971
Stock-based compensation	6,622	4,538
Other noncash items included in cost of operations	0	(560)
Change in fair value of contingent consideration	0	(640)
Changes in operating assets and liabilities, net of assets acquired and liabilities assumed in purchase transactions:
Accounts receivable	10,504	(9,486)
Other current assets	5,164	(1,184)
Other assets	677	1,254
Deferred taxes	(11,413)	(1,481)
Operating lease liability	(17,345)	(15,863)
Deferred revenue	28	(440)
Accounts payable, accrued expenses and other	21,584	16,989
Net cash provided by operating activities	40,913	26,900
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of imaging facilities	(4,300)	(3,000)
Equity investments at fair value	0	(143)
Purchase of property and equipment	(51,538)	(32,940)
Proceeds from sale of equipment	779	756
Proceeds from the sale of equity interests in a joint venture	0	132
Net cash used in investing activities	(55,059)	(35,195)
CASH FLOWS FROM FINANCING ACTIVITIES
Principal payments on notes and leases payable	(914)	(1,713)
Payments on term loan debt	(10,824)	(9,020)
Proceeds from sale of noncontrolling interest	0	5,275
Contribution from noncontrolling partner	0	750
Proceeds from revolving credit facility	215,900	144,900
Payments on revolving credit facility	(135,900)	(131,900)
Proceeds from issuance of common stock upon exercise of options	0	50
Net cash provided by financing activities	68,262	8,342
EFFECT OF EXCHANGE RATE CHANGES ON CASH	1	(8)
NET INCREASE IN CASH AND CASH EQUIVALENTS	54,117	39
CASH AND CASH EQUIVALENTS, beginning of period	40,165	10,389
CASH AND CASH EQUIVALENTS, end of period	94,282	10,428
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid during the period for interest	9,934	10,296
Equipment acquired and leasehold improvements	$ 30,800	$ 32,600