Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities
Net loss	$ (113,192)	$ (89,631)	$ (52,222)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization expense	15,949	10,600	8,195
Stock-based compensation	19,524	11,176	5,989
Provision for doubtful accounts on accounts receivable		171
Purchased premiums and interest on marketable securities	248	33
Non-cash interest expense			3
Changes in operating assets and liabilities:
Accounts receivable	(844)	2,361	(3,632)
Receivable from Roche	(1,604)	(403)
Inventory	(2,446)	(3,183)	(3,046)
Prepaid expenses and other current assets	1,305	(3,652)	(1,873)
Other assets	210	(267)	(282)
Accounts payable	5,060	(1,559)	3,119
Accrued expenses and other current liabilities	8,919	4,704	1,724
Deferred rent and other non-current liabilities	(1,688)	1,805	(133)
Deferred revenue	1,387	377	(578)
Roche related-party deferred revenue	5	3,742
Net cash used in operating activities	(67,167)	(63,726)	(42,736)
Investing activities
Purchases of property and equipment	(20,879)	(25,430)	(9,688)
Purchases of marketable securities and other investments	(107,456)	(114,756)
Proceeds from maturities of marketable securities	141,023
Change in restricted cash		(531)	861
Net cash provided by (used in) investing activities	12,688	(140,717)	(8,827)
Financing activities
Proceeds from issuance of restricted stock and stock option exercises	652	4,739	637
Payment of debt issuance costs	(319)
Payments of notes payable			(1,287)
Net cash provided by (used in) financing activities	333	250,126	(650)
Net decrease (increase) in cash and cash equivalents	(54,146)	45,683	(52,213)
Cash and cash equivalents at beginning of period	117,763	72,080	124,293
Cash and cash equivalents at end of period	63,617	117,763	72,080
Supplemental disclosure of cash flow information
Cash paid for interest	77		263
Supplemental disclosure of non-cash investing and financing activities
Acquisition of property and equipment included in accounts payable and accrued expenses	$ 2,029	6,822	$ 1,334
Roche [Member]
Financing activities
Proceeds from issuance of common stock, net of issuance costs		$ 245,387