Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Operating activities
Net loss	$ (46,453)	$ (17,307)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	4,466	3,069
Stock-based compensation expense	6,399	3,039
Amortization of premiums and discounts on marketable securities	14	78
Gain on disposal of long-lived assets	(139)
Changes in operating assets and liabilities:
Accounts receivable	2,348	(839)
Receivable from Roche	(2,863)	(1,965)
Inventory	178	1,249
Prepaid expenses and other current assets	(30)	1,429
Other assets	82	23
Accounts payable	278	2,582
Accrued expenses and other current liabilities	(1,780)	1,664
Deferred rent and other non-current liabilities	(571)	(563)
Deferred revenue	(120)	1,080
Roche related-party deferred revenue	(3,453)	(3,512)
Net cash used in operating activities	(41,644)	(9,973)
Investing activities
Purchases of property and equipment	(3,863)	(7,566)
Purchases of marketable securities and other investments	(4,996)	(31,809)
Proceeds from maturities of marketable securities	34,390	17,500
Net cash provided by (used in) investing activities	25,531	(21,875)
Financing activities
Proceeds from stock option exercises	1,571	143
Net cash provided by financing activities	1,571	143
Net decrease in cash and cash equivalents	(14,542)	(31,705)
Cash and cash equivalents at beginning of period	63,617	117,763
Cash and cash equivalents at end of period	49,075	86,058
Supplemental disclosure of non-cash investing and financing activities
Cash paid for interest	75
Acquisition of property and equipment included in accounts payable and accrued expenses	$ 696	$ 2,097