CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016
Cash flows from operating activities
Net income	$ 16,845		$ 4,435
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	3,496		3,483
Stock-based compensation	2,507		1,864
Amortization of premium (discount) on short term investment	17		(3)
Interest added to the principal balance of the non-recourse term notes due 2029	0		683
Amortization of debt issuance costs	687		699
Amortization of lease guarantee	(81)		0
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	3,120		(1,311)
Prepaid expenses and other current assets	(114)		(161)
Accounts payable	2,176		(242)
Accrued personnel-related expenses and other accrued liabilities	752		(625)
Accrued interest payable	(1,428)		(1,349)
Other long-term liabilities	5		(2)
Deferred revenue	(221)		(221)
Net cash provided by operating activities	27,761		7,250
Cash flows from investing activities
Maturities of marketable securities	26,387		27,671
Purchases of marketable securities	(3,992)		(15,978)
Net cash provided by investing activities	22,395		11,693
Cash flows from financing activities
Repurchase of common stock	0		(25,357)
Payment of principal on non-recourse notes due 2029	(7,752)		0
Payments of cash dividends to stockholders	(67)		(719)
Repurchase of shares to satisfy tax withholding	(553)		(442)
Proceeds from issuances of common stock, net	8		173
Net cash used in financing activities	(8,364)		(26,345)
Net increase (decrease) in cash and cash equivalents	41,792		(7,402)
Cash and cash equivalents at beginning of period	118,016	[1]	159,180
Cash and cash equivalents at end of period	159,808		151,778
Supplemental disclosure of cash flow information
Cash paid for interest	$ 13,522		$ 13,124

[1] Condensed consolidated balance sheet as of December 31, 2016 has been derived from audited consolidated financial statements.