Debt Securities - General Disclosures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Debt securities available for sale
Amortized Cost	$ 2,976,591		$ 2,976,591		$ 4,013,523
Gross Unrealized Gains	608		608		22,382
Gross Unrealized Losses	(232,553)		(232,553)		(54,654)
Fair Value	2,744,646		2,744,646		3,981,251
Debt securities held to maturity
Amortized Cost	953,012		953,012
Gross Unrealized Losses	(76,274)		(76,274)
Fair Value	876,738		876,738
Debt securities available for sale, Amortized Cost
Due in one year or less	191,190		191,190
Due after one year through five years	421,603		421,603
Due after five years through ten years	326,834		326,834
Due after ten years	2,036,964		2,036,964
Amortized Cost	2,976,591		2,976,591		4,013,523
Debt securities available for sale, Fair Value
Due in one year or less	189,295		189,295
Due after one year through five years	399,194		399,194
Due after five years through ten years	307,336		307,336
Due after ten years	1,848,821		1,848,821
Fair Value	2,744,646		2,744,646		3,981,251
Debt securities held to maturity, Amortized Cost
Due after one year through five years	48,232		48,232
Due after five years through ten years	66,107		66,107
Due after ten years	838,673		838,673
Amortised cost	953,012		953,012
Debt securities held to maturity, Fair Value
Due after one year through five years	46,533		46,533
Due after five years through ten years	61,995		61,995
Due after ten years	768,210		768,210
Fair value	876,738		876,738
Realized gains and losses on debt securities
Gross gains on debt securities	1	$ 499	114	$ 524
Gross (losses) on debt securities	(5)	(405)	(12)	(405)
Realized net gains (losses) on debt securities	(4)	$ 94	102	$ 119
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	2,001,930		2,001,930		2,676,734
Continuous unrealized losses existing for greater than 12 months, gross	627,993		627,993		106,443
Total, gross	2,629,923		2,629,923		2,783,177
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(157,307)		(157,307)		(49,847)
Continuous unrealized losses existing greater than 12 months, gross	(75,246)		(75,246)		(4,807)
Total, gross	(232,553)		(232,553)		(54,654)
Debt securities held to maturity, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	623,957		623,957
Continuous unrealized losses existing for greater than 12 months, gross	252,780		252,780
Total, gross	876,737		876,737
Debt securities held to maturity, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(53,749)		(53,749)
Continuous unrealized losses existing for greater than 12 months, gross	(22,525)		(22,525)
Total, gross	(76,274)		(76,274)
U.S. Treasury securities
Debt securities available for sale
Amortized Cost	151,222		151,222		166,768
Gross Unrealized Gains	1		1		41
Gross Unrealized Losses	(4,083)		(4,083)		(1,047)
Fair Value	147,140		147,140		165,762
Debt securities available for sale, Amortized Cost
Amortized Cost	151,222		151,222		166,768
Debt securities available for sale, Fair Value
Fair Value	147,140		147,140		165,762
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	21,976		21,976		163,653
Continuous unrealized losses existing for greater than 12 months, gross	124,094		124,094
Total, gross	146,070		146,070		163,653
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(154)		(154)		(1,047)
Continuous unrealized losses existing greater than 12 months, gross	(3,929)		(3,929)
Total, gross	(4,083)		(4,083)		(1,047)
Obligations of U.S. government corporations and agencies
Debt securities available for sale
Amortized Cost	29,867		29,867		37,579
Gross Unrealized Gains	53		53		891
Gross Unrealized Losses	(81)		(81)
Fair Value	29,839		29,839		38,470
Debt securities available for sale, Amortized Cost
Amortized Cost	29,867		29,867		37,579
Debt securities available for sale, Fair Value
Fair Value	29,839		29,839		38,470
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	17,078		17,078
Total, gross	17,078		17,078
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(81)		(81)
Total, gross	(81)		(81)
Obligations of states and political subdivisions
Debt securities available for sale
Amortized Cost	305,545		305,545		300,602
Gross Unrealized Gains	455		455		7,760
Gross Unrealized Losses	(18,388)		(18,388)		(1,493)
Fair Value	287,612		287,612		306,869
Debt securities available for sale, Amortized Cost
Amortized Cost	305,545		305,545		300,602
Debt securities available for sale, Fair Value
Fair Value	287,612		287,612		306,869
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	192,737		192,737		92,680
Continuous unrealized losses existing for greater than 12 months, gross	11,056		11,056
Total, gross	203,793		203,793		92,680
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(16,868)		(16,868)		(1,493)
Continuous unrealized losses existing greater than 12 months, gross	(1,520)		(1,520)
Total, gross	(18,388)		(18,388)		(1,493)
Commercial mortgage-backed securities
Debt securities available for sale
Amortized Cost	105,584		105,584		625,339
Gross Unrealized Gains					3,425
Gross Unrealized Losses	(7,222)		(7,222)		(13,766)
Fair Value	98,362		98,362		614,998
Debt securities held to maturity
Amortized Cost	492,924		492,924
Gross Unrealized Losses	(38,687)		(38,687)
Fair Value	454,237		454,237
Debt securities available for sale, Amortized Cost
Amortized Cost	105,584		105,584		625,339
Debt securities available for sale, Fair Value
Fair Value	98,362		98,362		614,998
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	91,564		91,564		389,078
Continuous unrealized losses existing for greater than 12 months, gross	6,798		6,798		85,905
Total, gross	98,362		98,362		474,983
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(6,560)		(6,560)		(10,186)
Continuous unrealized losses existing greater than 12 months, gross	(662)		(662)		(3,580)
Total, gross	(7,222)		(7,222)		(13,766)
Debt securities held to maturity, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	241,060		241,060
Continuous unrealized losses existing for greater than 12 months, gross	213,177		213,177
Total, gross	454,237		454,237
Debt securities held to maturity, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(19,840)		(19,840)
Continuous unrealized losses existing for greater than 12 months, gross	(18,847)		(18,847)
Total, gross	(38,687)		(38,687)
Residential mortgage-backed securities
Debt securities available for sale
Amortized Cost	1,599,774		1,599,774		2,095,104
Gross Unrealized Gains	50		50		8,889
Gross Unrealized Losses	(158,667)		(158,667)		(34,680)
Fair Value	1,441,157		1,441,157		2,069,313
Debt securities held to maturity
Amortized Cost	460,088		460,088
Gross Unrealized Losses	(37,587)		(37,587)
Fair Value	422,501		422,501
Debt securities available for sale, Amortized Cost
Amortized Cost	1,599,774		1,599,774		2,095,104
Debt securities available for sale, Fair Value
Fair Value	1,441,157		1,441,157		2,069,313
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	1,035,112		1,035,112		1,700,187
Continuous unrealized losses existing for greater than 12 months, gross	399,554		399,554		20,538
Total, gross	1,434,666		1,434,666		1,720,725
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(96,222)		(96,222)		(33,453)
Continuous unrealized losses existing greater than 12 months, gross	(62,445)		(62,445)		(1,227)
Total, gross	(158,667)		(158,667)		(34,680)
Debt securities held to maturity, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	382,897		382,897
Continuous unrealized losses existing for greater than 12 months, gross	39,603		39,603
Total, gross	422,500		422,500
Debt securities held to maturity, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(33,909)		(33,909)
Continuous unrealized losses existing for greater than 12 months, gross	(3,678)		(3,678)
Total, gross	(37,587)		(37,587)
Asset-backed securities
Debt securities available for sale
Amortized Cost	490,932		490,932		492,055
Gross Unrealized Gains					295
Gross Unrealized Losses	(22,803)		(22,803)		(164)
Fair Value	468,129		468,129		492,186
Debt securities available for sale, Amortized Cost
Amortized Cost	490,932		490,932		492,055
Debt securities available for sale, Fair Value
Fair Value	468,129		468,129		492,186
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	465,293		465,293		89,983
Continuous unrealized losses existing for greater than 12 months, gross	2,835		2,835
Total, gross	468,128		468,128		89,983
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(22,632)		(22,632)		(164)
Continuous unrealized losses existing greater than 12 months, gross	(171)		(171)
Total, gross	(22,803)		(22,803)		(164)
Corporate debt securities
Debt securities available for sale
Amortized Cost	293,667		293,667		296,076
Gross Unrealized Gains	49		49		1,081
Gross Unrealized Losses	(21,309)		(21,309)		(3,504)
Fair Value	272,407		272,407		293,653
Debt securities available for sale, Amortized Cost
Amortized Cost	293,667		293,667		296,076
Debt securities available for sale, Fair Value
Fair Value	272,407		272,407		293,653
Debt securities available for sale, Fair Value
Continuous unrealized losses existing for less than 12 months, gross	178,170		178,170		241,153
Continuous unrealized losses existing for greater than 12 months, gross	83,656		83,656
Total, gross	261,826		261,826		241,153
Debt securities available for sale, Unrealized Losses
Continuous unrealized losses existing for less than 12 months, gross	(14,790)		(14,790)		(3,504)
Continuous unrealized losses existing greater than 12 months, gross	(6,519)		(6,519)
Total, gross	$ (21,309)		$ (21,309)		$ (3,504)