Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		$ 12,618			$ 12,618
Investment securities losses (gains), net	$ (362)		$ (11)		(437)	$ (90)
Personnel expense	(106,994)		(111,350)		(211,020)	(225,551)
Interest income	(645)		(776)		(1,163)	(1,332)
Other comprehensive income (loss)	7,082	(16,811)	15,054	$ 16,209	(9,729)	31,263
Ending Balance	2,889				2,889
Investment Securities AFS
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	23,754	41,325	19,620	3,989	41,325	3,989
Other comprehensive income (loss) before reclassifications	7,978		21,641		(16,002)	48,060
Investment securities losses (gains), net	(24)		(3,096)		16	(9,214)
Personnel expense	0		0		0	0
Other expense	0		0		0	0
Interest income	645		776		1,163	1,332
Income tax (expense) benefit	(2,277)		(4,841)		3,574	(10,066)
Other comprehensive income (loss)	6,322		14,481		(11,249)	30,112
Ending Balance	30,076	23,754	34,101	19,620	30,076	34,101
Defined Benefit Pension and Postretirement Obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(27,947)	(28,707)	(36,595)	(37,172)	(28,707)	(37,172)
Other comprehensive income (loss) before reclassifications	0		0		0	0
Investment securities losses (gains), net	0		0		0	0
Personnel expense	(37)		(38)		(74)	(75)
Other expense	1,050		803		2,100	1,610
Interest income	0		0		0	0
Income tax (expense) benefit	(253)		(192)		(506)	(385)
Other comprehensive income (loss)	760		573		1,519	1,150
Ending Balance	(27,187)	(27,947)	(36,021)	(36,595)	(27,187)	(36,021)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(4,193)	12,618	(16,974)	(33,183)	12,618	(33,183)
Other comprehensive income (loss) before reclassifications	7,978		21,641		(16,002)	48,060
Investment securities losses (gains), net	(24)		(3,096)		16	(9,214)
Personnel expense	(37)		(38)		(74)	(75)
Other expense	1,050		803		2,100	1,610
Interest income	645		776		1,163	1,332
Income tax (expense) benefit	(2,530)		(5,032)		3,068	(10,450)
Other comprehensive income (loss)	7,082	(16,811)	15,054	16,209	(9,729)	31,263
Ending Balance	$ 2,889	$ (4,193)	$ (1,920)	$ (16,974)	$ 2,889	$ (1,920)