Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income	$ 45,885	$ 126,959	$ 11,001
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	5,772	5,002	4,258
Gain on sale of equipment			(248)
Deferred income taxes	11,209	(82,085)	519
Stock-based compensation expense	7,784	5,672	5,179
Provision for doubtful accounts			106
Provision for excess and obsolete inventory	2,205	8,135	1,051
Changes in operating assets & liabilities:
Accounts receivable	(3,877)	(23,573)	(14,135)
Inventories	(10,512)	(10,567)	(6,572)
Prepaid expenses and other current assets	(1,436)	(3,866)	(1,056)
Accounts payable and other current liabilities	(703)	25,000	810
Deferred revenue	6,055	7,079	2,467
Income taxes	196	14	102
Other assets and liabilities	(15,613)	(1,486)	(12,270)
Net cash provided by (used in) operating activities	46,965	56,284	(8,788)
Cash flows from investing activities
Proceeds from sale of equipment			270
Expenditures for property, plant and equipment and capitalized software	(4,715)	(7,285)	(2,506)
Net cash used in investing activities	(4,715)	(7,285)	(2,236)
Cash flows from financing activities
Net settlement on restricted stock grants	(1,419)	(1,184)	(11)
Financing fees and other expenses			(146)
Proceeds from Employee Stock Purchase Plan	871	739	277
Proceeds from exercise of stock options	1,734	15,515	2,227
Net cash provided by financing activities	1,186	15,070	2,347
Effect of exchange rate changes on cash and cash equivalents	586	(844)	507
Net increase (decrease) in cash, cash equivalents and restricted cash	44,022	63,225	(8,170)
Cash, cash equivalents and restricted cash at beginning of period	140,880	77,655	85,825
Cash, cash equivalents and restricted cash at end of period	184,902	140,880	77,655
Supplemental disclosure of cash flow information
Income taxes	858	583	525
Interest	$ 5,470	$ 5,315	$ 4,815