CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net income	$ 133,131	$ 137,113
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	29,499	0
Depreciation and amortization	10,400	10,404
Stock-based compensation	1,568	2,747
Amortization of debt discount and issuance costs	5,789	5,895
Amortization of discount on short-term investments	(1,739)	(224)
Amortization of lease guarantee	(243)	(243)
Loss on write-off of property and equipment	104	0
Loss on extinguishment of debt	0	5,745
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	14,075	5,404
Prepaid expenses and other current assets	466	241
Other assets	(11)	0
Accounts payable	24	(492)
Accrued personnel-related expenses and other accrued liabilities	107	(695)
Accrued interest payable	(2,491)	(4,145)
Other long-term liabilities	(126)	4
Net cash provided by operating activities	190,553	161,754
Cash flows from investing activities
Maturities of marketable securities	160,925	71,375
Purchases of marketable securities	(230,922)	(22,262)
Net cash provided by (used in) investing activities	(69,997)	49,113
Cash flows from financing activities
Repurchase of shares to satisfy tax withholding	(81)	(3,082)
Payments of principal on senior secured term loans	0	(230,000)
Payments of cash dividends to stockholders	(11)	(72)
Proceeds from issuances of common stock, net	618	454
Distributions to noncontrolling interest	(10,553)	(2,888)
Net cash provided by (used in) financing activities	(10,027)	(235,588)
Net increase (decrease) in cash and cash equivalents	110,529	(24,721)
Cash and cash equivalents at beginning of period	62,417	73,336
Cash and cash equivalents at end of period	172,946	48,615
Supplemental disclosure of cash flow information
Cash paid for interest	$ 10,674	$ 17,622