Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities
Net loss	$ (85,444)	$ (52,764)
Adjustments to reconcile net loss to cash used in operating activities
Depreciation	1,069	927
Stock-based compensation expense	7,641	4,741
Amortization of (discount) premium on marketable securities	(461)	259
Amortization of debt discount and debt issuance costs	3,811	1,190
Premium paid on securities purchased	(4)	(580)
Changes in operating assets and liabilities:
Accounts receivable	(4,650)
Inventory	(1,505)
Prepaid expenses, other current and long-term assets	429	1,456
Accounts payable	(629)	736
Accrued expenses and other current and long-term liabilities	(2,283)	1,796
Net cash used in operating activities	(82,026)	(42,239)
Cash flows from investing activities
Purchases of property and equipment	(561)	(1,682)
Purchases of marketable securities	(65,215)	(118,320)
Sale and redemption of marketable securities	196,072	135,363
Net cash provided by investing activities	130,296	15,361
Cash flows from financing activities
Proceeds from the issuance of 2024 convertible notes		201,250
Payment of debt issuance costs		(6,470)
Payments on notes payable	(5,000)	(3,333)
Payments of public offering costs		(95)
Proceeds from the exercise of stock options	1,777	1,457
Proceeds from employee stock purchase plan	1,129	453
Net cash (used in) provided by financing activities	(2,094)	193,262
Net increase in cash, cash equivalents, and restricted cash	46,176	166,384
Cash, cash equivalents, and restricted cash at beginning of period	128,389	31,395
Cash, cash equivalents, and restricted cash at end of period	174,565	197,779
Supplemental disclosures of cash flow information
Cash paid for interest	4,015	921
Supplemental disclosures of non-cash financing activities
Purchases of property and equipment in accounts payable and accrued expenses	$ 79	$ 66