Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net loss	$ (8,981)	$ (29,722)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	119	54
Stock-based compensation expense	2,820	3,864
Changes in assets and liabilities
Prepaid expenses and other assets	92	(9,065)
Accounts payable	(690)	220
Accrued and other liabilities	(1,368)	(79)
Net cash used in operating activities	(8,008)	(34,728)
Cash flows from investing activities
Inducement on build-to-suit lease obligation	1,516
Net cash used in investing activities	1,516
Cash flows from financing activities
Proceeds from issuance of common stock in connection with employee benefit plans	35	1,034
Net cash provided by financing activities	35	1,034
Net increase (decrease) in cash, cash equivalents, and restricted cash	(6,457)	(33,694)
Cash, cash equivalents, and restricted cash at beginning of period	83,529	201,153
Cash, cash equivalents, and restricted cash at end of period	77,072	167,459
Supplemental disclosure of noncash items
Build-to-suit lease transaction	$ 5,428	$ 8,174