CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net income	$ 218,798	$ 133,131
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	44,689	29,499
Depreciation and amortization	10,382	10,400
Stock-based compensation	1,251	1,568
Amortization of debt discount and issuance costs	6,230	5,789
Amortization of discount on short-term investments	(343)	(1,739)
Amortization of lease guarantee	135	(243)
Loss on write-off of property and equipment	0	104
Changes in fair values of equity investments	(39,245)	0
Other non-cash items	14	0
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	(12,723)	14,075
Prepaid expenses and other current assets	264	466
Other assets	0	(11)
Accounts payable	613	24
Accrued personnel-related expenses and other accrued liabilities	252	107
Accrued interest payable	(2,484)	(2,491)
Other long-term liabilities	0	(126)
Net cash provided by operating activities	227,833	190,553
Cash flows from investing activities
Maturities of marketable securities	86,000	160,925
Purchases of marketable securities	(12,943)	(230,922)
Purchases of equity investments	(72,500)	0
Purchases of property and equipment	(13)	0
Net cash provided by (used in) investing activities	544	(69,997)
Cash flows from financing activities
Repurchase of shares to satisfy tax withholding	(83)	(81)
Payments of cash dividends to stockholders	0	(11)
Proceeds from issuances of common stock, net	421	618
Net proceeds from the issuance of variable interest entity's equity	344	0
Distributions to noncontrolling interest	(27,962)	(10,553)
Net cash used in financing activities	(27,280)	(10,027)
Net increase in cash and cash equivalents	201,097	110,529
Cash and cash equivalents at beginning of period	278,096	62,417
Cash and cash equivalents at end of period	479,193	172,946
Supplemental disclosure of cash flow information
Cash paid for interest	$ 9,933	$ 10,674