CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount	$ 776	$ 831
Debt Securities, Available-for-sale, Amortized Cost	137,124	102,258
Debt Securities, Available-for-sale, Amortized Cost, Noncurrent	$ 587,981	$ 390,417
Preferred stock par value, in dollars per share	$ 0.01	$ 0.01
Preferred stock, shares authorized	400,000	400,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock par value, in dollars per share	$ 0.002	$ 0.002
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	175,481,000	175,790,000
Common stock, shares outstanding	175,481,000	175,790,000
Debt Securities, Available-for-sale, Allowance for Credit Loss, Current	$ 0	$ 0
Debt Securities, Available-for-sale, Allowance for Credit Loss, Noncurrent	$ 0	$ 0