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	$ 18,722	$ 31,816	$ 32,547
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,910	4,290	3,734
Loss on disposal of fixed assets	152	150
Stock-based compensation expense	11,046	5,807	3,392
Deferred income taxes	(1,817)	(1,198)	(65)
Provision for doubtful accounts	57	1,609	52
Provision for inventory	4,419	695	654
Accretion to amortized cost of investments	(371)
Changes in operating assets and liabilities:
Accounts receivable	2,914	2,674	(6,201)
Inventories	(7,577)	(6,521)	(1,738)
Prepaid expenses, other current and long-term assets	899	(1,454)	(898)
Accounts payable	(1,671)	3,890	(5,059)
Accrued expenses, other current and long-term liabilities	1,313	(1,313)	1,582
Income taxes payable	922	367	(3,552)
Net cash provided by operating activities	34,918	40,812	24,448
Cash flows from investing activities:
Proceeds from maturity of investments	46,000	41,500	46,500
Purchase of investments	(91,601)	(45,000)	(39,249)
Purchase of property and equipment	(4,656)	(8,980)	(14,014)
Net cash (used in) investing activities	(50,257)	(12,480)	(6,763)
Cash flows from financing activities:
Repurchase of common stock	(30,000)		(25,000)
Tax payments related to witholdings on vested restricted stock	(1,790)
Proceeds from exercise of equity awards	2,886	314	1,007
Net cash (used in) provided by financing activities	(28,904)	314	(23,993)
Exchange rate impact on cash	29	349	(138)
Increase (Decrease) in cash and cash equivalents	(44,214)	28,995	(6,446)
Cash and cash equivalents at beginning of period	133,256	104,261	110,707
Cash and cash equivalents at end of period	89,042	133,256	104,261
Supplemental disclosure of cash flow information:
Cash paid for income taxes	5,560	15,088	22,826
Non-cash Investing Activities:
Purchases of property and equipment included in accounts payable and accrued expenses	351	1,891	1,257
Build-to-suit lease agreement			$ 1,723