Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net loss	$ (54,220)	$ (45,923)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	600	457
Amortization of deferred financing costs and debt discount	153	151
Amortization and accretion of premium or discount on available-for-sale investments, net	60	275
Stock-based compensation	11,515	7,415
Unrealized foreign exchange loss	365	0
Changes in operating assets and liabilities
Prepaid, current and other assets	1,765	791
Accounts payable and other current liabilities	(6,024)	(2,998)
Net cash used in operating activities	(45,786)	(39,832)
Cash flows from investing activities
Purchase of available-for-sale investments	(54,427)	(19,228)
Proceeds from sales and maturities of investments	24,801	24,815
Purchase of property, plant and equipment	(2,594)	(459)
Net cash (used in) provided by investing activities	(32,220)	5,128
Cash flows from financing activities
Proceeds from sale of common stock, net	122,046	2,043
Proceeds related to issuance of stock for stock-based compensation arrangements, net	665	120
Net cash provided by financing activities	122,711	2,163
Net change in cash and cash equivalents	44,705	(32,541)
Beginning of period	197,945	91,060
End of period	242,650	58,519
Supplemental disclosures
Income taxes paid	0	1,789
Interest paid	$ 540	1,096
Build-to-suit lease transaction