Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income		$ 173	$ 7,546
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		33,830	30,911
Deferred taxes		(3,209)	(1,571)
Provisions and releases for bad debt and sales-related allowances		703	6,401
Provision for inventory obsolescence		2,928	1,465
Stock-based compensation expense		18,555	17,893
Non-cash accretion of interest expense on convertible notes and imputed financing obligation		7,677	7,459
Change in fair value of contingent consideration		(12,775)	899
Net change in derivative assets and liabilities		(7,100)	1,012
Other non-cash charges and gains		256	979
Changes in operating assets and liabilities, net of effect of acquired businesses		(3,807)	(33,984)
Net cash provided by operating activities		37,231	39,010
Cash flows from investing activities:
Purchases of short-term investments		0	(62,431)
Proceeds from sales and maturities of short-term investments		14,042	85,306
Purchases of restricted investments	[1]	0	(10,011)
Purchases, net of proceeds from sales, of property and equipment		(6,435)	(5,711)
Businesses purchased, net of cash acquired		(252)	(13,512)
Net cash provided by (used for) investing activities	[1]	7,355	(6,359)
Cash flows from financing activities:
Proceeds from issuance of common stock		5,010	6,643
Purchases of treasury stock and net share settlements		(29,028)	(41,326)
Repayment of debt assumed through business acquisitions		(1,618)	(1,489)
Contingent consideration payments related to businesses acquired		(698)	(1,294)
Net cash used for financing activities		(26,334)	(37,466)
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash equivalents		(1,812)	3,259
Increase (decrease) in cash, cash equivalents, and restricted cash equivalents		16,440	(1,556)
Cash, cash equivalents, and restricted cash equivalents at beginning of period	[1]	202,876	165,455
Cash, cash equivalents, and restricted cash equivalents at end of period	[1]	$ 219,316	$ 163,899

[1] Certain prior period amounts have been revised due to the implementation of ASU 2016-18. See Note 1 for details.