Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities
Net loss	$ (17,307)	$ (16,965)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	3,069	2,206
Stock-based compensation expense	3,039	1,688
Amortization of premiums and discounts on marketable securities	78
Changes in operating assets and liabilities:
Accounts receivable	(839)	(779)
Receivable from Roche	(1,965)
Inventory	1,249	316
Prepaid expenses and other current assets	1,429	(398)
Other assets	23	(75)
Accounts payable	2,582	(991)
Accrued expenses and other current liabilities	1,664	3,918
Deferred rent and other non-current liabilities	(563)	320
Deferred revenue	1,080	(157)
Roche related-party deferred revenue	(3,512)
Net cash used in operating activities	(9,973)	(10,917)
Investing activities
Purchases of property and equipment	(7,566)	(2,304)
Purchases of marketable securities and other investments	(31,809)
Proceeds from maturities of marketable securities	17,500
Increase in restricted cash		(1,037)
Net cash used in investing activities	(21,875)	(3,341)
Financing activities
Proceeds from issuance of restricted stock and stock option exercises	143	3,878
Net cash provided by financing activities	143	3,878
Net decrease in cash and cash equivalents	(31,705)	(10,380)
Cash and cash equivalents at beginning of period	117,763	72,080
Cash and cash equivalents at end of period	86,058	61,700
Supplemental disclosure of non-cash investing and financing activities
Acquisition of property and equipment included in accounts payable and accrued expenses	$ 2,097	$ 5,352