Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Accounts and accrued income receivable, allowances	$ 12,924	$ 13,994
Debt securities, amortized cost	7,109,478	6,121,004
Debt securities, allowance for credit losses	109	132
Pledged securities included in debt securities	$ 92,784	$ 93,586
Preferred stock, par value	$ 0.00001	$ 0.00001
Preferred stock, shares authorized	500	500
Preferred stock, outstanding	0	0
Common stock, par value	$ 0.00001	$ 0.00001
Common stock, shares authorized	300,000	300,000
Common stock, shares outstanding	109,741	110,353