Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Available-for-sale, amortized cost	$ 7,834,082	$ 7,684,889
Investment securities - held-to-maturity, fair value	$ 2,547,576	$ 2,601,188
Preferred stock, shares authorized (in shares)	2,000	2,000
Preferred stock, shares issued (in shares)	231	231
Preferred stock, shares outstanding (in shares)	231	231
Common stock, stated value (in dollars per share)	$ 1.00	$ 1.00
Authorized and unissued common shares reserved for issuance (in shares)	600,000	600,000
Common stock, shares issued (in shares)	293,330	292,655
Common stock, shares outstanding (in shares)	293,330	292,655