CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
OPERATING ACTIVITIES:
Net income	$ 65,315	$ 56,586
Adjustments to reconcile net income to net cash provided by operating activities:
Change in fair value of contingent consideration	1,204	(2,140)
Stock compensation expense	4,085	3,863
Excess tax benefit of stock options exercised	(5,061)	(8,092)
Depreciation	12,739	11,756
Amortization	4,979	3,347
Deferred income taxes	11,921	16,051
Changes in operating assets and liabilities, net of effect of acquisitions and divestitures:
Accounts receivable	(14,493)	(11,615)
Accounts payable	2,101	(433)
Accrued liabilities	12,623	799
Deferred revenues	1,029	(34)
Other assets and liabilities	3,119	(4,503)
Net cash provided by operating activities	99,561	65,585
INVESTING ACTIVITIES:
Payments for acquisitions, net of cash acquired	(28,182)	(19,543)
Purchases of short-term investments	(2)	(1,240)
Proceeds from sale of business and other assets	0	389
Capital expenditures	(17,049)	(11,692)
Net cash used in investing activities	(45,233)	(32,086)
FINANCING ACTIVITIES:
Repayment of long-term debt and other obligations	(8,571)	(24,100)
Borrowings on senior credit facility	185,434	139,290
Repayments on senior credit facility	(238,290)	(225,334)
Payments on capital lease obligations	(640)	(463)
Purchase and cancellation of treasury stock	(2,945)	0
Proceeds from other issuance of common stock	12,494	14,811
Excess tax benefit of stock options exercised	5,061	8,092
Net cash used in financing activities	(47,457)	(87,704)
Effect of exchange rate changes on cash	880	1,808
Net increase/ (decrease) in cash and cash equivalents	7,751	(52,397)
Cash and cash equivalents at beginning of period	22,511	77,053
Cash and cash equivalents at end of period	30,262	24,656
NON-CASH ACTIVITIES:
Net issuance of obligations for acquisitions	$ 14,883	$ 730