CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net income	$ 78,923	$ 60,386	$ 45,942
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	16,362	13,422	12,160
Stock-based compensation expense	9,358	5,964	4,872
Deferred income taxes	19,453	(4,475)	7,402
Loss on disposal of assets	319	60	1,199
Impairment of goodwill and intangibles	4,370	1,511
Changes in operating assets and liabilities, net of acquisitions:
Receivables	(362)	(26,906)	(14,083)
Prepaid expenses and other assets	(10,257)	(26,973)	1,034
Prepaid income taxes	(2,519)	(7,006)	1,641
Accounts payable and accrued expenses	(6,577)	19,666	9,182
Income tax payable	511	(3,499)	84
Net amounts due to/from governmental entities	(996)	176	(1,961)
Net cash provided by operating activities	108,585	32,326	67,472
Investing activities
Cash acquired from business combination, net of cash paid	7,702	(64,598)	(23,156)
Purchases of property, building and equipment	(32,993)	(10,176)	(16,009)
Advanced payments on acquisitions	0		(11,215)
Net cash used in investing activities	(25,291)	(74,774)	(50,380)
Financing activities
Proceeds from line of credit	303,943	96,000	38,000
Payments on line of credit	(319,743)	(39,000)	(49,000)
Proceeds from employee stock purchase plan	1,342	1,026	912
Payments on debt	(4,975)	(260)	(238)
Payments on deferred financing fees	(1,884)	0	0
Noncontrolling interest distributions	(12,134)	(11,382)	(9,413)
Purchase of additional controlling interest	(412)	(1,488)	0
Sale of noncontrolling interest	4,208	251	356
Withholding taxes paid on stock-based compensation	(7,125)	(3,114)	(584)
Net cash (used in) provided by financing activities	(36,780)	42,033	(19,967)
Change in cash	46,514	(415)	(2,875)
Cash at beginning of period	2,849	3,264	6,139
Cash at end of period	49,363	2,849	3,264
Supplemental disclosures of cash flow information
Interest paid	9,067	3,853	3,123
Income taxes paid	5,703	25,199	11,533
Non-cash financing and investing activity:
Accrued capital expenditures	3,449	0	0
Consideration transferred for a business combination	795,412	0	0
Purchase of additional controlling interests	$ 7,705	$ 0	$ 0