Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017
Operating activities
Net loss	$ (39,310)		$ (53,729)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,343		1,242
Amortization of deferred financing costs	59		325
Amortization of deferred compensation for services	101		91
Amortization of premium on investment securities	(256)		1
Stock-based compensation	5,028		4,899
Non-cash interest expense relating to loan payable	54
Changes in operating assets and liabilities:
Accounts receivable	10,766
Prepaid expenses and other assets	1,192		(2,961)
Accounts payable	(706)		(451)
Accrued compensation and benefits	(1,026)		(562)
Accrued and other liabilities	(2,064)		498
Net cash used in operating activities	(24,819)		(50,647)
Investing activities
Proceeds from maturities of investments	56,050		75,434
Sales and redemptions of investments	850		10,482
Purchases of investments	(119,021)		(44,748)
Purchases of property and equipment	(55)		(1,907)
Net cash (used in) provided by investing activities	(62,176)		39,261
Financing activities
Proceeds from loan payable, net of issuance costs	49,292
Proceeds from underwritten public offering, net of issuance costs	53,770
Proceeds from issuance of common stock under stock plans	301		424
Net cash provided by financing activities	103,363		424
Net decrease in cash and cash equivalents	16,368		(10,962)
Cash and cash equivalents at beginning of period	75,383	[1]	74,598
Cash and cash equivalents at end of period	91,751		$ 63,636
Supplementary disclosure of non-cash financing information:
Issuance of derivative in connection with issuance of loan payable	$ 546

[1] Derived from the audited consolidated financial statements included in the Company’s Annual Report on Form 10K for the year ended December 31, 2017.