CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities
Net income	$ 177,177	$ 86,080
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	35,823	18,940
Depreciation and amortization	6,921	7,080
Stock-based compensation	810	1,079
Amortization of debt discount and issuance costs	4,110	3,820
Amortization of discount on short-term investments	(336)	(1,124)
Amortization of lease guarantee	(135)	(162)
Changes in fair values of equity investments	(68,613)	0
Other non-cash items	6	0
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	(2,975)	15,723
Prepaid expenses and other current assets	317	390
Accounts payable	185	1,128
Accrued personnel-related expenses and other accrued liabilities	(15)	343
Accrued interest payable	0	(2)
Operating lease liability	0	(144)
Net cash provided by operating activities	153,275	133,151
Cash flows from investing activities
Maturities of marketable securities	82,000	57,875
Purchases of marketable securities	(12,943)	(111,935)
Purchases of equity investments	(60,000)	0
Purchases of property and equipment	(13)	0
Net cash provided by (used in) investing activities	9,044	(54,060)
Cash flows from financing activities
Repurchase of shares to satisfy tax withholding	(72)	(74)
Payments of cash dividends to stockholders	0	(11)
Proceeds from issuances of common stock, net	422	529
Net proceeds from the issuance of variable interest entity's equity	344	0
Distributions to noncontrolling interest	(27,962)	0
Net cash provided by (used in) financing activities	(27,268)	444
Net increase in cash and cash equivalents	135,051	79,535
Cash and cash equivalents at beginning of period	278,096	62,417
Cash and cash equivalents at end of period	413,147	141,952
Supplemental disclosure of cash flow information
Cash paid for interest	$ 4,967	$ 5,461