Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net income (loss)	$ 4,816	$ (3,118)
Adjustments for non-cash operating items:
Stock-based compensation	14,211	13,372
Change in fair value of contingent purchase consideration	5,959	4,000
Depreciation on property and equipment	2,416	1,531
Change in deferred income taxes	2,696	(1,402)
Amortization of debt discount and debt issuance costs	85	3,910
Excess tax benefits from stock-based compensation	(2,490)
Amortization of deferred revenue		(1,411)
Other non-cash items		73
Changes in operating assets and liabilities:
Receivable from collaboration partner	204,965	58,124
Prepaid expenses and other current assets	(6,050)	(520)
Other non-current assets	(1,049)	(1,335)
Accounts payable, accrued expenses and other current liabilities	(26,869)	(17,587)
Interest payable		1,698
Current taxes payable	(32,565)
Other non-current liabilities	(438)	(113)
Net cash provided by operating activities	165,687	57,222
Cash flows from investing activities:
Purchases of property and equipment	(9,328)	(956)
Change in restricted cash		(1,574)
Net cash used in investing activities	(9,328)	(2,530)
Cash flows from financing activities:
Principal repayment of borrowings under Revolving Credit Facility	(75,000)
Proceeds from issuance of common stock under equity incentive and stock purchase plans	7,677	11,502
Excess tax benefits from stock-based compensation	2,490
Reduction of build-to-suit lease obligation	(18)	(227)
Principal repayment of Convertible Notes		(8)
Net cash (used in) provided by financing activities	(64,851)	11,267
Net increase in cash and cash equivalents	91,508	65,959
Cash and cash equivalents at beginning of period	225,853	502,677
Cash and cash equivalents at end of period	317,361	568,636
Non-cash investing and financing activities:
Property and equipment expenditures incurred but not yet paid	$ 964	918
Interest capitalized during construction period for build-to-suit lease transactions		$ 527