CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018
Cash flows (used in) provided by operating activities:
Net (loss) income		$ (14,048)	$ 39,193
Adjustments to reconcile net (loss) income to net cash (used in) provided by operating activities:
Depreciation and amortization		4,885	4,668
Stock-based compensation		4,559	4,324
Deferred income taxes		(5,379)	(10,253)
Increase in provision for doubtful accounts		1,255	(6)
Excess and obsolete inventory valuation adjustment		(1,264)	(1,443)
Changes in operating assets and liabilities:
Accounts receivable		24,225	47,265
Inventory		(23,075)	3,079
Prepaid expenses and other assets		(1,859)	(452)
Prepaid income taxes		(28)	463
Accounts payable		(7,865)	3,170
Accrued expenses and other current liabilities		(6,387)	(5,113)
Accrued income taxes		(759)	(245)
Deferred revenue		(5,380)	(2,282)
Net cash (used in) provided by operating activities		(31,120)	82,368
Cash flows used in investing activities:
Purchases of property and equipment		(3,764)	(4,501)
Net cash used in investing activities		(3,764)	(4,501)
Cash flows (used in) provided by financing activities:
Principal repayments of debt		(1,656)	(1,651)
Proceeds from exercise of stock options		2,168	10,147
Employee taxes paid related to net share settlement of equity awards		(1,004)
Payments of dividends and equitable adjustments		(2,090)	(5,486)
Follow-on offering selling shareholders profit disgorgement			3,811
Payments of initial public offering costs			(1,148)
Net cash (used in) provided by financing activities		(2,582)	5,673
Effect of exchange rate changes on cash and cash equivalents		50	(429)
Net (decrease) increase in cash, cash equivalents and restricted cash		(37,416)	83,111
Cash, cash equivalents and restricted cash at beginning of period		281,606	260,820
Cash, cash equivalents and restricted cash at end of period	[1]	244,190	343,931
Supplemental disclosures of cash flow information:
Cash paid for interest		9,539	8,834
Cash paid for income taxes		2,857	3,554
Supplemental disclosures of non-cash operating, investing and financing activities:
Purchases of property and equipment included in accounts payable		1,626	373
Prepaid expenses and other current assets included in accounts payable		76	405
Unpaid equitable adjustments included in accrued expenses and other current liabilities		1,246	5,174
Release of customer incentives included in accounts receivable and accrued expenses and other current liabilities		$ 5,604	$ 5,932

[1] See Note 2 of the accompanying notes for a reconciliation of the ending balance of cash, cash equivalents and restricted cash shown in these condensed consolidated statements of cash flows.