CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017
Cash flows from operating activities
Net income	$ 86,946		$ 51,991
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	6,936		6,991
Stock-based compensation	3,621		4,934
Amortization of debt discount and issuance costs	4,028		1,401
Loss on extinguishment of debt	3,137		830
Amortization of premium (discount) on short-term investments	(160)		6
Amortization of lease guarantee	(162)		(162)
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	(2)		(14,949)
Prepaid expenses and other current assets	178		124
Accounts payable	(543)		149
Accrued personnel-related expenses and other accrued liabilities	(1,539)		242
Accrued interest payable	(805)		(725)
Other long-term liabilities	4		10
Deferred revenue	0		(442)
Net cash provided by operating activities	101,639		50,400
Cash flows from investing activities
Maturities of marketable securities	54,875		36,387
Purchases of marketable securities	(19,284)		(11,969)
Net cash provided by investing activities	35,591		24,418
Cash flows from financing activities
Repurchase of shares to satisfy tax withholding	(2,840)		(847)
Payments of principal on senior secured term loans	(120,000)		0
Payments of cash dividends to stockholders	(55)		(107)
Proceeds from issuances of common stock, net	454		185
Payment of principal on non-recourse notes due 2029	0		(64,431)
Distributions to noncontrolling interest	(899)		0
Net cash used in financing activities	(123,340)		(65,200)
Net increase in cash and cash equivalents	13,890		9,618
Cash and cash equivalents at beginning of period	73,336	[1]	118,016
Cash and cash equivalents at end of period	87,226		127,634
Supplemental disclosure of cash flow information
Cash paid for interest	$ 10,913		$ 24,310

[1] *Condensed consolidated balance sheet as of December 31, 2017 has been derived from audited consolidated financial statements.