Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net income	$ 17,034	$ 45,885	$ 126,959
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Depreciation and amortization	7,880	5,772	5,002
Deferred income taxes	3,304	11,209	(82,085)
Stock-based compensation expense	8,173	7,784	5,672
Provision for doubtful accounts	818
Provision for excess and obsolete inventory	2,794	2,205	8,135
Changes in operating assets & liabilities:
Accounts receivable	(6,002)	(3,877)	(23,573)
Inventories	(17,953)	(10,512)	(10,567)
Prepaid expenses and other current assets	(104)	(1,436)	(3,866)
Accounts payable and other current liabilities	(19,150)	(703)	25,000
Deferred revenue	6,672	6,055	7,079
Income taxes	(162)	196	14
Other assets and liabilities	(16,898)	(15,613)	(1,486)
Net cash (used in) provided by operating activities	(13,594)	46,965	56,284
Cash flows from investing activities
Expenditures for property, plant and equipment and capitalized software	(11,969)	(4,715)	(7,285)
Net cash used in investing activities	(11,969)	(4,715)	(7,285)
Cash flows from financing activities
Net settlement on restricted stock grants	(1,632)	(1,419)	(1,184)
Repurchase of common stock	(17,744)
Proceeds from Employee Stock Purchase Plan	863	871	739
Proceeds from exercise of stock options	5,105	1,734	15,515
Net cash (used in) provided by financing activities	(13,408)	1,186	15,070
Effect of exchange rate changes on cash and cash equivalents	603	586	(844)
Net (decrease) increase in cash, cash equivalents and restricted cash	(38,368)	44,022	63,225
Cash, cash equivalents and restricted cash at beginning of period	184,902	140,880	77,655
Cash, cash equivalents and restricted cash at end of period	146,534	184,902	140,880
Supplemental disclosure of cash flow information
Income taxes	1,028	858	583
Interest	$ 5,207	$ 5,470	$ 5,315