Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net income		$ 115,549	$ 141,216	$ 107,416
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		154,452	140,926	91,958
Non-cash interest expense, including write-off of deferred financing costs on redeemed debt		7,355	10,717	8,595
Non-cash stock-based compensation expense		15,950	12,944	4,433
Excess tax benefit from stock-based compensation	[1]	(3,728)	(4,315)	(759)
Provision for deferred income taxes		13,756	6,533	5,127
Other non-cash items		5,955	8,009	9,305
(Gains) losses on sales of assets, including impairment charges on discontinued operations		(6,434)	(1,492)	11,714
Changes in assets and liabilities, net of acquisitions:
Accounts receivable		163,773	(204,330)	(177,313)
Inventories		(12,621)	13,481	15,448
Other assets, current and long-term portion		(14,221)	6,248	(6,773)
Accounts payable and accrued expenses		(87,494)	72,514	76,285
Billings in excess of costs and earnings		(34,320)	(8,227)	15,651
Book overdrafts		9,911	6,363	116
Other liabilities, current and long-term portion		(4,872)	(185)	11,305
Net cash provided by operating activities		323,011	200,402	172,508
Cash flows (used in) provided by investing activities:
Cash paid for acquisitions, net of cash acquired		(345,543)	(148,567)	(119,459)
Proceeds from disposal of business, net of cash divested		0	(2,997)	97,728
Capital expenditures		(109,254)	(126,288)	(79,686)
Proceeds from sale of property and equipment		16,655	15,858	7,385
Proceeds from sale or redemption of investments		0	14,956	0
Payments for other investments, net		(1,120)	(16,173)	(284)
Net cash used in investing activities		(439,262)	(263,211)	(94,316)
Cash flows provided by (used in) financing activities:
Proceeds from credit facilities		2,385,971	1,149,040	959,183
Repayments of credit facilities		(1,939,612)	(1,249,601)	(885,183)
Proceeds from issuance of senior notes		0	400,000	0
Repayment of senior notes, including convertible notes		(202,325)	(150,000)	0
Repayments of other borrowings		(15,700)	(27,705)	(21,455)
Payments of capital lease obligations		(51,587)	(43,040)	(21,060)
Repurchase of common stock		0	0	(75,000)
Proceeds from stock-based awards, net of tax withholdings		1,113	8,355	5,013
Excess tax benefit from stock-based compensation		3,728	4,315	759
Payments of acquisition-related contingent consideration		(60,341)	(18,683)	(33,936)
Payments of financing costs, including call premiums on extinguishment of debt		(2,572)	(13,688)	(117)
Net cash provided by (used in) financing activities		118,675	58,993	(71,796)
Effect of currency translation on cash		(1,292)	(24)	91
Net increase (decrease) in cash and cash equivalents		1,132	(3,840)	6,487
Cash and cash equivalents - beginning of period		22,927	26,767	20,280
Cash and cash equivalents - end of period		24,059	22,927	26,767
Supplemental cash flow information:
Interest paid		42,979	37,531	27,074
Income taxes paid, net of refunds		76,975	79,504	58,968
Supplemental disclosure of non-cash information:
Equipment acquired under capital lease		64,618	86,330	60,648
2011 Convertible Notes [Member]
Supplemental disclosure of non-cash information:
Premium shares, conversion of convertible notes		155,744
Earn-Out Arrangements [Member]
Supplemental disclosure of non-cash information:
Acquisition-related contingent consideration, new business combinations		33,612	32,451	66,700
Equipment [Member]
Supplemental disclosure of non-cash information:
Equipment acquired under financing arrangements		$ 11,105	$ 24,244	$ 6,009

[1] Excess tax benefits, which represent cash flows from tax deductions in excess of the tax effect of compensation expense associated with exercised stock options and vested restricted shares, are classified as financing cash flows in the Company’s consolidated statements of cash flows.