Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net income	$ (15,128)	$ (19,111)	$ (13,769)
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation	6,461	6,353	5,642
Amortization of securities discount	(23)	(200)	(393)
Amortization of intangible assets	1,707	1,740	1,547
Amortization of other	885	827	426
Accretion of asset retirement obligations	$ 147	136	126
(Gain) Loss on disposal of equipment		9	139
Provision for inventory reserves and purchase order commitments	$ 0	306	5,606
Stock-based compensation	15,262	16,827	15,473
Excess tax benefit from share-based arrangements	0	0	(384)
Changes in operating assets and liabilities:
Accounts receivable	16,109	(9,776)	8,023
Inventories	(13,061)	(4,830)	(12,230)
Prepaid expenses and other current assets	1,913	(316)	2,758
Other assets	(616)	(638)	(673)
Accounts payable	(6)	3,172	(8,827)
Accrued expenses	620	(3,462)	(647)
Deferred product and services income	(4,139)	2,064	(10,390)
Other liabilities	(1,701)	245	822
Net cash provided by operating activities	8,430	(6,654)	(6,751)
Cash flows from investing activities:
Capital expenditures	(2,587)	(2,823)	(7,933)
Purchase of patents and Intangibles	0	0	(5,000)
Purchase of investments in securities	(233,636)	(230,033)	(229,740)
Proceeds from maturities of investments	246,252	231,889	232,128
Net cash provided by (used in) investing activities	10,029	(967)	(10,545)
Cash flows from financing activities:
Proceeds from notes payable	20,480	20,480	8,120
Repayment of notes payable	(20,480)	(20,480)	(4,000)
Proceeds from issuance of common stock for stock option exercises	332	4,279	12,808
Tax payment for issuance of common stock from release of restricted stock units	(2,333)	(2,950)	(3,434)
Excess tax benefit from exercise of stock options	0	0	384
Payments for Repurchase of Common Stock	(21,438)	(19,270)	0
Net cash provided by financing activities	(23,439)	(17,941)	13,878
Net increase (decrease) in cash and cash equivalents	(4,980)	(25,562)	(3,418)
Cash and cash equivalents at beginning of period	67,988	93,550	96,968
Cash and cash equivalents at end of period	63,008	67,988	93,550
Supplemental disclosures of cash flow information:
Income taxes paid	325	396	343
Other non-cash changes:
Systems transferred from (to) inventory to (from) equipment and other assets	338	302	6,641
Sale Leaseback Transaction, Historical Cost	$ 0	$ 2,460	$ 0