CONSOLIDATED STATEMENTS OF CASH FLOWS Non-Cash Activities - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Significant Noncash Transactions [Line Items]
Unrealized (loss) gain on available-for-sale securities	$ (118)	$ 241	$ 342
Net change in accounts payable and accrued expenses related to purchases of property and equipment	(1,468)	(530)	3,490
Cash paid for income tax	36,269	46,602	17,771
Common Stock Issued to Board of Directors and Scientific Advisory Board that was Earned and Accrued for in Previous Period [Member]
Other Significant Noncash Transactions [Line Items]
Other significant noncash transaction, value of consideration received	$ 300	$ 300	$ 300