Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net loss	$ (226,505)		$ (137,125)	$ (83,352)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation and amortization	1,311		1,542	1,359
Amortization of premium on investment securities	3,174		3,703	2,333
Stock-based compensation expense	22,858		9,333	4,974
Change in reserve for uncertain tax position	(365)
Revaluation of convertible preferred stock warrant liability				(24)
Unrealized (gain) loss on foreign currency forward contracts			114	(261)
Changes in operating assets and liabilities:
Receivables from collaborations	(943)		252	353
Prepaid research and development	(15,290)		(745)	718
Prepaid expenses and other current assets	1,001		(1,383)	(1,187)
Prepaid and other long-term assets	3,619		(15,559)	396
Accounts payable	(4,061)		10,763	(1,773)
Accrued compensation and employee benefits	2,054		893	650
Accrued research and development	11,650		(3,565)	12,742
Accrued and other liabilities	1,531		(261)	(834)
Deferred revenue	(9,569)		31,374	1,169
Other long-term liabilities	2,281		(42)	(878)
Net cash used in operating activities	(207,252)		(100,706)	(63,615)
Investing activities
Purchases of property and equipment	(4,746)		(1,629)	(933)
Increase in restricted cash (Development Partner)	(341)
Purchases of investments	(266,068)		(332,171)	(219,813)
Proceeds from sales of investments			2,603	8,009
Proceeds from maturities of investments	324,100		192,045	92,001
Net cash provided by/ (used in) investing activities	52,945		(139,152)	(120,736)
Financing activities
Proceeds from public offering of common stock, net of underwriters discount	272,216		175,185	251,865
Payment of public offering costs	(882)		(564)	(5,883)
Proceeds from issuance of common stock pursuant to equity award plans	11,948		4,978	2,529
Net cash provided by financing activities	283,282		179,599	248,511
Net increase (decrease) in cash and cash equivalents	128,974		(60,259)	64,160
Cash and cash equivalents at beginning of year	57,514		117,773	53,613
Cash and cash equivalents at end of year	186,488	[1]	57,514	117,773
Noncash investing and financing activities:
Net change in accrued offering cost	238
Net change in accounts payable related to purchase of property and equipment	$ 5		$ 89	$ 165

[1] Amounts include the assets and liabilities of a consolidated variable interest entity (“VIE”). Portola's interests and obligations with respect to the VIE's assets and liabilities are limited to those accorded to Portola in its agreement with the VIE. See Note 8, “Asset Acquisition and License Agreements,” to these consolidated financial statements.