CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Preferred stock	Common stock	Surplus	Treasury stock	Retained earnings	Retained earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated other comprehensive loss
Beginning balance at Dec. 31, 2022	$ 4,796,838	$ (544)	$ 412,500	$ 60,797	$ 1,902,474	$ (304)	$ 2,849,007	$ (544)	$ (427,636)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	499,146						499,146
Other comprehensive income (loss), net of tax	(215,087)								(215,087)
Cash dividends declared on common stock	(73,304)						(73,304)
Dividends on Series D and E preferred stock	(20,973)						(20,973)
Stock-based compensation	24,532				24,532
Common stock issued for:
Exercise of stock options	2,216			54	2,162
Restricted stock awards	(1,662)			296	(296)	(1,662)
Employee stock purchase plan	2,418			34	2,384
Director compensation plan	2,033			63	1,970
Ending balance at Sep. 30, 2023	5,015,613		412,500	61,244	1,933,226	(1,966)	3,253,332		(642,723)
Beginning balance at Jun. 30, 2023	5,041,912		412,500	61,219	1,923,623	(1,966)	3,120,626		(474,090)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	164,198						164,198
Other comprehensive income (loss), net of tax	(168,633)								(168,633)
Cash dividends declared on common stock	(24,501)						(24,501)
Dividends on Series D and E preferred stock	(6,991)						(6,991)
Stock-based compensation	8,130				8,130
Common stock issued for:
Restricted stock awards	0			13	(13)
Employee stock purchase plan	816			12	804
Director compensation plan	682				682
Ending balance at Sep. 30, 2023	5,015,613		412,500	61,244	1,933,226	(1,966)	3,253,332		(642,723)
Beginning balance at Dec. 31, 2023	5,399,526		412,500	61,269	1,943,806	(2,217)	3,345,399		(361,231)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	509,683						509,683
Other comprehensive income (loss), net of tax	69,054								69,054
Cash dividends declared on common stock	(85,394)						(85,394)
Dividends on Series D and E preferred stock	(20,973)						(20,973)
Stock-based compensation	27,568				27,568
Common stock issued for:
Acquisition of Macatawa Bank Corporation	499,239			4,702	494,537
Exercise of stock options	25			1	24
Restricted stock awards	(3,877)			533	(529)	(3,881)
Employee stock purchase plan	2,440			26	2,414
Director compensation plan	2,423			15	2,408
Ending balance at Sep. 30, 2024	6,399,714		412,500	66,546	2,470,228	(6,098)	3,748,715		(292,177)
Beginning balance at Jun. 30, 2024	5,536,628		412,500	61,825	1,964,645	(5,760)	3,615,616		(512,198)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	170,001						170,001
Other comprehensive income (loss), net of tax	220,021								220,021
Cash dividends declared on common stock	(29,911)						(29,911)
Dividends on Series D and E preferred stock	(6,991)						(6,991)
Stock-based compensation	9,461				9,461
Common stock issued for:
Acquisition of Macatawa Bank Corporation	499,239			4,702	494,537
Restricted stock awards	(338)			10	(10)	(338)
Employee stock purchase plan	797			9	788
Director compensation plan	807				807
Ending balance at Sep. 30, 2024	$ 6,399,714		$ 412,500	$ 66,546	$ 2,470,228	$ (6,098)	$ 3,748,715		$ (292,177)