CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net income	$ 40,019	$ 30,330
Adjustments to reconcile net income to net cash provided by operating activities:
Deferred income taxes	8,508	0
Depreciation and amortization	3,539	3,468
Stock-based compensation	605	2,169
Amortization of debt discount and issuance costs	1,889	2,092
Amortization of discount on short-term investments	(356)	(100)
Amortization of lease guarantee	(81)	(81)
Loss on extinguishment of debt	0	3,137
Changes in operating assets and liabilities:
Receivables from collaborative arrangements	24,647	14,705
Prepaid expenses and other current assets	147	(196)
Accounts payable	133	(535)
Accrued personnel-related expenses and other accrued liabilities	166	(1,702)
Accrued interest payable	(2,489)	(3,375)
Operating lease liability	(72)	0
Other long-term liabilities	0	2
Net cash provided by operating activities	76,655	49,914
Cash flows from investing activities
Maturities of marketable securities	27,875	31,875
Purchases of marketable securities	(102,042)	(5,362)
Net cash provided by (used in) investing activities	(74,167)	26,513
Cash flows from financing activities
Repurchase of shares to satisfy tax withholding	(65)	(2,611)
Payments of principal on senior secured term loans	0	(120,000)
Payments of cash dividends to stockholders	(8)	(38)
Proceeds from issuances of common stock, net	319	114
Distributions to noncontrolling interest	0	(90)
Net cash provided by (used in) financing activities	246	(122,625)
Net increase (decrease) in cash and cash equivalents	2,734	(46,198)
Cash and cash equivalents at beginning of period	62,417	73,336
Cash and cash equivalents at end of period	65,151	27,138
Supplemental disclosure of cash flow information
Cash paid for interest	$ 5,218	$ 8,941