CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017		Jun. 30, 2016
Cash flows from operating activities
Net income	$ 51,991		$ 19,032
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	6,991		6,967
Stock-based compensation	4,934		4,705
Amortization of debt issuance costs	1,401		1,414
Loss (gain) on extinguishment of debt	830		(1,752)
Amortization of premium (discount) on short-term investments	6		(14)
Amortization of lease guarantee	(162)		(28)
Interest added to the principal balance of the non-recourse term notes due 2029	0		855
Realized gain on sale of marketable securities, net	0		1
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	(14,949)		(9,589)
Prepaid expenses and other current assets	124		76
Other assets	0		(40)
Accounts payable	149		(681)
Accrued personnel-related expenses and other accrued liabilities	242		(627)
Accrued interest payable	(725)		(88)
Other long-term liabilities	10		(78)
Deferred revenue	(442)		(443)
Net cash provided by operating activities	50,400		19,710
Cash flows from investing activities
Maturities of marketable securities	36,387		44,101
Purchases of marketable securities	(11,969)		(59,893)
Sales of marketable securities	0		2,995
Purchases of property and equipment	0		(8)
Net cash provided by (used in) investing activities	24,418		(12,805)
Cash flows from financing activities
Payment of principal on non-recourse notes due 2029	(64,431)		0
Repurchase of shares to satisfy tax withholding	(847)		(597)
Payments of cash dividends to stockholders	(107)		(843)
Proceeds from issuances of common stock, net	185		335
Repurchase of common stock	0		(44,331)
Repurchase of convertible subordinated notes due 2023	0		(8,095)
Proceeds from capped-call options	0		391
Net cash used in financing activities	(65,200)		(53,140)
Net increase (decrease) in cash and cash equivalents	9,618		(46,235)
Cash and cash equivalents at beginning of period	118,016	[1]	159,180
Cash and cash equivalents at end of period	127,634		112,945
Supplemental disclosure of cash flow information
Cash paid for interest	$ 24,310		$ 24,132

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