Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities
Net loss	$ (115,118)	$ (76,582)
Adjustments to reconcile net loss to net cash used in operating activities:
Change in fair value of contingent consideration	1,001	2,188
Depreciation and amortization	4,747	3,509
Stock-based compensation expense	20,926	21,482
Other non-cash items	1,563	269
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,722)	(1,059)
Accounts payable	(3,132)	(418)
Accrued expenses and other liabilities	2,497	1,098
Deferred revenue	7,669	13,716
Deferred rent	469	(480)
Net cash used in operating activities	(81,100)	(36,277)
Investing activities
Restricted cash	209	359
Purchase of property and equipment	(6,057)	(2,568)
Purchases of marketable securities	(80,845)	(261,440)
Proceeds from maturities of marketable securities	226,825	62,680
Net cash provided by (used in) investing activities	140,132	(200,969)
Financing activities
Cash paid for contingent purchase price consideration	(2,025)
Proceeds from public offering of common stock, net of issuance costs		477,179
Proceeds from issuance of common stock	1,353	5,521
Net cash (used in) provided by financing activities	(672)	482,700
Increase in cash and cash equivalents	58,360	245,454
Cash and cash equivalents at beginning of period	164,269	347,845
Cash and cash equivalents at end of period	222,629	593,299
Non-cash investing and financing activities:
Construction financing lease obligation	24,725
Purchases of property and equipment included in accounts payable and accrued expenses	$ 909	$ 524