Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 102,450	$ 81,678	$ 57,217
Adjustments to reconcile net income to cash flows:
Depreciation and amortization	31,848	24,665	22,061
Non-cash deferred revenue	(4,887)	(25,822)	(12,372)
Restructuring expenses		1,138	15,573
Increase in inventory reserve	4,892	7,885	3,119
Stock based compensation	8,914	7,766	5,599
Deferred income tax provision	6,925	8,556	19,736
Toll tax	2,105
Other	581	160	(141)
Changes in assets and liabilities:
Trade receivables	40,651	(5,120)	(14,378)
Inventories	(13,283)	(23,679)	(32,721)
Prepaid expenses and other current assets	(8,123)	(729)	4,268
Accounts payable and other current liabilities	(20,114)	12,056	11,779
Deferred revenue and advance payments	985	41,962	12,178
Other non-current assets and liabilities	(5,347)	(3,961)	(5,331)
Discontinued operations:
Non-current liabilities	2,858	7,517
Net cash used in discontinued operations	(1,440)	(516)	(1,536)
Net cash provided by operating activities	149,015	133,556	85,051
Cash flows from investing activities:
Capital expenditures	(52,143)	(49,714)	(62,491)
Proceeds from sale of assets		13	2,308
Proceeds from sale of business	2,836
Acquisition of business and equity investment, net of cash acquired		(24,275)
Other			(56)
Net cash used in investing activities	(49,307)	(73,976)	(60,239)
Cash flows from financing activities:
Repayments		(30,000)	(30,000)
Proceeds from stock options exercised	4,781	4,941	5,816
Debt issuance costs		(2,515)
Net cash provided by/(used in) financing activities	4,781	(27,574)	(24,184)
Effect of exchange rate changes on cash and cash equivalents	4,654	(1,839)	(2,172)
Net increase/(decrease) in cash and cash equivalents	109,143	30,167	(1,544)
Cash and cash equivalents at beginning of year	74,141	43,974	45,518
Cash and cash equivalents at end of year	183,284	74,141	43,974
Supplemental disclosure:
Interest paid, net of capitalized interest	1,270	425	1,340
Income taxes paid, net of refunds received	$ 45,744	$ 18,210	$ 5,731