CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net income	$ 78,952	$ 40,019
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	15,932	8,508
Depreciation and amortization	3,463	3,539
Stock-based compensation	435	605
Amortization of debt discount and issuance costs	2,032	1,889
Amortization of discount on short-term investments	(272)	(356)
Amortization of lease guarantee	(81)	(81)
Changes in fair values of equity investments	(21,915)	0
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	(2,707)	24,647
Prepaid expenses and other current assets	140	147
Accounts payable	112	133
Accrued personnel-related expenses and other accrued liabilities	(126)	166
Accrued interest payable	(2,484)	(2,489)
Operating lease liability	0	(72)
Net cash provided by operating activities	73,481	76,655
Cash flows from investing activities
Maturities of marketable securities	54,000	27,875
Purchases of marketable securities	(12,943)	(102,042)
Purchases of equity investments	(25,000)	0
Purchases of property and equipment	(13)	0
Net cash provided by (used in) investing activities	16,044	(74,167)
Cash flows from financing activities
Repurchase of shares to satisfy tax withholding	(55)	(65)
Payments of cash dividends to stockholders	0	(8)
Proceeds from issuances of common stock, net	225	319
Distributions to noncontrolling interest	(15,810)	0
Net cash provided by (used in) financing activities	(15,640)	246
Net increase in cash and cash equivalents	73,885	2,734
Cash and cash equivalents at beginning of period	278,096	62,417
Cash and cash equivalents at end of period	351,981	65,151
Supplemental disclosure of cash flow information
Cash paid for interest	$ 4,967	$ 5,218