CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating Activities:
Net loss	$ (24,370)	$ (13,810)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	1,309	980
Amortization of net premiums on marketable securities	427	99
Deferred rent	(195)	213
Non-cash stock-based compensation	1,932	1,040
Realized gains on marketable securities	0	(615)
Other	146	3
Changes in operating assets and liabilities:
Restricted cash	297	1,081
Accounts receivable - billed	1,018	(2,559)
Accounts receivable - unbilled	(1,096)	(1,125)
Prepaid expenses and other assets	(2,491)	(1,516)
Accounts payable and accrued expenses	(7,574)	(4,007)
Deferred revenue	107	(215)
Net cash used in operating activities	(30,490)	(20,431)
Investing Activities:
Capital expenditures	(4,864)	(889)
Proceeds from maturities of marketable securities	29,450	10,590
Purchases of marketable securities	(6,798)	0
Net cash provided by investing activities	17,788	9,701
Financing Activities:
Principal payments on capital leases	(16)	(6)
Principal payments on notes payable	(164)	(168)
Changes in restricted cash	0	(1)
Net proceeds from sales of common stock	193,619	0
Proceeds from the exercise of stock options and employee stock purchases	2,057	1,345
Net cash provided by financing activities	195,496	1,170
Effect of exchange rate on cash and cash equivalents	(79)	10
Net increase (decrease) in cash and cash equivalents	182,715	(9,550)
Cash and cash equivalents at beginning of period	32,335	119,471
Cash and cash equivalents at end of period	215,050	109,921
Supplemental disclosure of non-cash activities:
Property and equipment purchases included in accounts payable and accrued expenses	3,118	214
Supplemental disclosure of cash flow information:
Cash payments of interest	$ 31	$ 52