Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating activities
Net loss	$ (56,274)	$ (24,787)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	1,013	215
Depreciation and amortization	2,283	1,710
Stock-based compensation expense	10,143	5,432
Other non-cash items	868	130
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,271)	(2)
Accounts payable	(2,195)	(331)
Accrued expenses and other liabilities	211	88
Deferred revenue	9,222	(6,344)
Deferred rent	234	(270)
Net cash used in operating activities	(36,766)	(24,159)
Investing activities
Purchase of property and equipment	(3,894)	(1,156)
Purchases of marketable securities	(28,175)	(223,020)
Proceeds from maturities of marketable securities	96,515	31,200
Net cash provided by (used in) investing activities	64,446	(192,976)
Financing activities
Proceeds from issuance of common stock	639	2,464
Net cash provided by financing activities	639	2,464
Increase (decrease) in cash and cash equivalents	28,319	(214,671)
Cash and cash equivalents at beginning of period	164,269	347,845
Cash and cash equivalents at end of period	192,588	133,174
Non-cash investing and financing activities:
Construction financing lease obligation	12,513
Purchases of property and equipment included in accounts payable and accrued expenses	$ 1,086	$ 1,125