Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 17,786	$ 13,239
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,343	13,110
Deferred taxes	(7,714)	1,281
Provisions for bad debt and sales-related allowances	2,169	199
Tax benefit (release) from employee stock plans	2,474	(367)
Excess tax benefit from stock-based compensation	(2,637)	(495)
Provisions for inventory obsolescence	2,361	2,122
Stock-based compensation	12,442	9,433
Contingent consideration payment related to business acquired	(618)
Non-cash acquisition-related compensation costs	465	456
Other non-cash charges and credits	162	1,038
Changes in operating assets and liabilities	444	(21,636)
Net cash provided by operating activities	41,677	18,380
Cash flows from investing activities:
Purchases of short-term investments	(17,781)	(28,542)
Proceeds from sales and maturities of short-term investments	34,513	36,193
Purchases, net of proceeds from sales, of property and equipment	(27,324)	(3,801)
Businesses purchased, net of cash acquired, and post-acquisition non-competition agreements	(4,533)	(44,533)
Proceeds from notes receivable of acquired businesses		5,216
Net cash used for investing activities	(15,125)	(35,467)
Cash flows from financing activities:
Proceeds from issuance of common stock	7,906	15,041
Purchases of treasury stock and net settlement of restricted stock	(17,837)	(9,456)
Repayment of acquired business debt	(1,621)	(6,666)
Contingent consideration payments related to businesses acquired	(9,998)	(252)
Excess tax benefit from stock-based compensation	2,637	495
Net cash used for financing activities	(18,913)	(838)
Effect of foreign exchange rate changes on cash and cash equivalents	(1,625)	(308)
Increase (decrease) in cash and cash equivalents	6,014	(18,233)
Cash and cash equivalents at beginning of period	283,996	120,058
Cash and cash equivalents at end of period	$ 290,010	$ 101,825