QUARTERLY FINANCIAL INFORMATION (UNAUDITED) - STATEMENTS OF CASH FLOWS (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (84,413)	$ (4,161)	$ 1,637	$ (17,734)	$ (81,128)	$ (7,478)	$ (328)	$ (17,537)	$ (16,097)	$ (17,865)	$ (20,258)	$ (25,343)	$ (104,671)	$ (106,471)	$ (327,091)
Income from discontinued operations, net of income taxes					(15)	378	572			572		950		935	(7,974)
Loss from continuing operations	(84,413)	(4,161)	1,637	(17,734)	(81,113)	(7,856)	(900)	(17,537)	(16,097)	(18,437)	(20,258)	(26,293)	(104,671)	(107,406)	(319,117)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	9,665	9,632	9,825	10,137	10,160	11,339	11,660	11,728	19,962	23,388	29,594	34,727	39,259	44,887	46,343
Provision for doubtful accounts				2,360				4,249	4,517	5,780	6,850	7,546	9,422	13,727	12,854
Stock-based compensation expense				2,164				2,948	5,080	5,425	8,693	7,552	12,930	9,763	11,134
Benefit for deferred income taxes				(6,050)					(5,548)		(7,179)		26,248	4,031	(48,926)
Amortization of debt issuance costs				1,952				766	3,874	1,618	6,348	2,845	8,876	4,921	3,371
Loss (gain) on extinguishment of debt						6,041	(10)			(10)		6,031		6,031	7,237
Gain on sale and disposal of fixed assets				(672)				(704)	(1,196)	(1,213)	(1,664)	(1,901)	(2,059)	(5,055)	(2,384)
Changes in operating assets and liabilities, net of effects of acquired companies:
Net accounts receivable				15,367				20,522	5,061	23,102	1,772	28,336	(12,585)	17,612	(13,625)
Inventories				(4,653)				(685)	(4,113)	(2,614)	(5,870)	(6,085)	(913)	253	2,520
Other current assets				39				(2,055)	947	(602)	1,510	421	661	849	3,913
Income taxes				849				(8,640)	345	(9,671)	(584)	20,994	121	18,725	(40,152)
Accounts payable				6,333				(13,287)	(1,267)	14,608	(348)	4,259	(3,562)	(3,133)	8,084
Accrued expenses and accrued interest payable				(683)				6,560	(8,488)	393	(9,690)	(6,881)	(12,929)	(3,045)	(6,264)
Accrued compensation related costs				(19,171)				(23,037)	(6,234)	(24,396)	(6,942)	(25,975)	16,843	(12,006)	6,877
Other liabilities				(1,901)				(223)	(3,176)	(1,230)	(3,240)	(2,060)	(2,271)	(5,797)	6,940
Net cash provided by operating activities - continuing operations								(19,395)		16,141		43,516	30,105	70,521	64,612
Net cash used in operating activities - discontinued operations										(850)		(1,425)		(1,425)	(5,098)
Net cash provided by operating activities				(11,663)				(19,395)	(6,333)	15,291	(1,008)	42,091	30,105	69,096	59,514
Cash flows from investing activities:
Purchase of property, plant and equipment				(2,348)				(6,364)	(6,433)	(9,963)	(11,237)	(13,943)	(16,355)	(21,148)	(27,620)
Purchase of equipment leased to third parties under operating leases				(629)				(608)	(1,333)	(1,190)	(3,714)	(1,914)	(6,000)	(2,476)	(4,632)
Restricted cash				12				4	24	2,676	56	2,716	(1,016)	1,615	(54)
Purchase of company-owned life insurance investment				(555)				(2,543)	(555)	(2,543)	(555)	(2,543)	(555)	(2,543)	(2,544)
Proceeds from sale of property, plant and equipment				2,179				1,136	3,216	1,922	4,185	2,647	4,909	5,960	4,954
Other investing activities, net								(10)		(10)		(10)		(10)	(50)
Net cash used in investing activities - continuing operations								(8,385)		(9,108)		(13,047)	(1,882)	(18,602)	(40,161)
Net cash provided by investing activities - discontinued operations										850		1,425		1,425	4,987
Net cash used in investing activities				(1,341)				(8,385)	(5,081)	(8,258)	(11,265)	(11,622)	(1,882)	(17,177)	(35,174)
Cash flows from financing activities:
Borrowings under term loan												274,400	420	274,400
Repayment of term loan				(5,625)				(4,219)	(11,250)	(8,438)	(19,688)	(14,063)	(28,545)	(19,688)	(14,063)
Borrowings under revolving credit agreement				49,500					110,000		140,965	20,000	156,965	23,000	155,000
Repayments under revolving credit agreement				(31,500)					(85,000)		(105,965)	(144,000)	(151,965)	(155,000)	(93,000)
Payment of senior notes												(200,000)		(200,000)
Payment of employee taxes on stock-based compensation				(1,338)				(259)	(1,339)	(259)	(1,367)	(271)	(1,477)	(288)	(2,212)
Payment on sellers notes and other contingent consideration				(3,498)				(4,536)	(3,808)	(5,817)	(4,633)	(7,751)	(5,197)	(9,128)	(13,561)
Payment of capital lease obligations				(278)				(230)	(572)	(494)	(873)	(702)	(1,210)	(979)	(1,110)
Payment of debt issuance costs and fees								(1,767)	(2,863)	(1,767)	(2,863)	(15,832)	(2,863)	(15,832)	(8,340)
Net cash (used in) provided by financing activities - continuing operations				7,261				(11,011)	5,168	(16,775)	5,576	(88,219)	(33,872)	(103,515)	22,714
(Decrease) increase in cash and cash equivalents				(5,743)				(38,791)	(6,246)	(9,742)	(6,697)	(57,750)	(5,649)	(51,596)	47,054
Cash and cash equivalents, at beginning of year	460	911	1,414	7,157	1,003	49,011	19,962	58,753	7,157	58,753	7,157	58,753	7,157	58,753	11,699
Cash and cash equivalents, at end of year	$ 1,508	$ 460	$ 911	1,414	$ 7,157	$ 1,003	$ 49,011	19,962	911	49,011	460	1,003	1,508	7,157	58,753
Cash paid during the period for:
Interest				12,218				3,759	24,387	15,111	36,807	30,850	48,437	42,345	26,070
Income taxes (refunds received) paid				(849)				168	(345)	1,077	584	(33,821)	725	(35,092)	18,106
Non-cash financing and investing activities:
Additions to property, plant and equipment acquired through finance obligations				623				162	669	213	1,299	269	1,484	374	3,743
Retirements of financed property, plant and equipment								1,663	135	2,157	135	2,228	811	2,381	1,434
Purchase of property, plant and equipment in accounts payable				$ 1,337				$ 747	$ 1,100	$ 998	$ 865	$ 1,900	$ 2,119	$ 728	$ 2,746