Condensed 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	$ (66,319)	$ (46,349)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	104	106
Stock-based compensation expense	7,522	5,377
Changes in assets and liabilities
Prepaid expenses and other assets	(7,122)	(3,636)
Accounts payable	1,194	(940)
Accrued and other liabilities	8,063	547
Income taxes payable	(247)
Net cash used in operating activities	(56,805)	(44,895)
Cash flows from investing activities
Purchase of property and equipment	(1,009)	(90)
Change in restricted cash	(2,380)
Net cash used in investing activities	(3,389)	(90)
Cash flows from financing activities
Proceeds from issuance of common stock in connection with employee benefit plans	2,399	413
Net cash provided by financing activities	2,399	413
Net increase (decrease) in cash and cash equivalents	(57,795)	(44,572)
Cash and cash equivalents at beginning of period	201,153	182,069
Cash and cash equivalents at end of period	143,358	$ 137,497
Supplemental disclosure
Income taxes paid	375
Supplemental disclosure of noncash items
Build-to-suit lease hold improvements	1,219
Build-to-suit lease transaction	$ 8,174