Condensed Consolidated Balance Sheets (Parenthetical) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Available-for-sale debt securities, amortized cost	$ 33,932,000
Available-for-sale debt securities, allowance for credit losses	0
Allowance for credit losses	$ 2,510,000	$ 566,000
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	64,716,000	63,622,000
Common stock, shares outstanding (in shares)	50,530,000	49,620,000
Treasury stock, shares (in shares)	14,186,000	14,002,000