Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Statement of Comprehensive Income [Abstract]
Net income	$ 86,824	$ 91,007	$ 161,086	$ 185,307
AFS investment securities
Net unrealized gains (losses)	(65,038)	7,978	(168,321)	(16,002)
Unrealized (losses) on AFS securities transferred to HTM securities	0	0	(67,604)	0
Amortization of net unrealized losses on AFS securities transferred to HTM securities	3,273	645	4,381	1,163
Reclassification adjustment for net losses (gains) realized in net income	8	(24)	(12)	16
Income tax (expense) benefit	15,998	(2,277)	59,096	3,574
Other comprehensive income (loss) on AFS securities	(45,758)	6,322	(172,460)	(11,249)
Defined benefit pension and postretirement obligations
Amortization of prior service cost	(81)	(37)	(163)	(74)
Amortization of actuarial loss	74	1,050	147	2,100
Income tax (expense) benefit	2	(253)	4	(506)
Other comprehensive income (loss) on pension and postretirement obligations	(6)	760	(12)	1,519
Total other comprehensive income (loss)	(45,764)	7,082	(172,472)	(9,729)
Comprehensive income (loss)	$ 41,060	$ 98,088	$ (11,386)	$ 175,578