Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Valuation allowance			$ 3,281
Recurring
Assets, Fair Value Disclosure [Abstract]
U.S. Treasury securities		$ 73,200	72,867
U.S. government agency securities		92,327	79,692
Mortgage-backed securities		1,618,580	1,463,907
State and municipal securities		1,036,619	1,714,453
Agency-backed securities		146,460	152,972
Corporate notes and other		63,378	56,104
Total investment securities available-for-sale		3,030,564	3,539,995
Other Investments		65,194	63,291
Other assets		262,156	134,040
Total assets at fair value		3,357,914	3,737,326
Liabilities at fair value: [Abstract]
Other liabilities		202,366	87,613
Total liabilities at fair value		202,366	87,613
Recurring | Quoted market prices in an active market (Level 1)
Assets, Fair Value Disclosure [Abstract]
U.S. Treasury securities		0	0
U.S. government agency securities		0	0
Mortgage-backed securities		0	0
State and municipal securities		0	0
Agency-backed securities		0	0
Corporate notes and other		0	0
Total investment securities available-for-sale		0	0
Other Investments		0	0
Other assets		0	0
Total assets at fair value		0	0
Liabilities at fair value: [Abstract]
Other liabilities		0	0
Total liabilities at fair value		0	0
Recurring | Models with significant observable market parameters (Level 2)
Assets, Fair Value Disclosure [Abstract]
U.S. Treasury securities		73,200	72,867
U.S. government agency securities		92,327	79,692
Mortgage-backed securities		1,618,580	1,463,907
State and municipal securities		1,021,852	1,698,550
Agency-backed securities		146,460	152,972
Corporate notes and other		63,378	56,104
Total investment securities available-for-sale		3,015,797	3,524,092
Other Investments		25,438	25,135
Other assets		262,156	134,040
Total assets at fair value		3,303,391	3,683,267
Liabilities at fair value: [Abstract]
Other liabilities		202,366	87,613
Total liabilities at fair value		202,366	87,613
Recurring | Models with significant unobservable market parameters (Level 3)
Assets, Fair Value Disclosure [Abstract]
U.S. Treasury securities		0	0
U.S. government agency securities		0	0
Mortgage-backed securities		0	0
State and municipal securities		14,767	15,903
Agency-backed securities		0	0
Corporate notes and other		0	0
Total investment securities available-for-sale		14,767	15,903
Other Investments		39,756	38,156
Other assets		0	0
Total assets at fair value		54,523	54,059
Liabilities at fair value: [Abstract]
Other liabilities		0	0
Total liabilities at fair value		0	0
Nonrecurring
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value		62,436	61,964
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other real estate owned		27,182	29,487
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	35,254	32,477
Nonrecurring | Quoted market prices in an active market (Level 1)
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value		0	0
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other real estate owned		0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	0	0
Nonrecurring | Models with significant observable market parameters (Level 2)
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value		0	0
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other real estate owned		0	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	0	0
Nonrecurring | Models with significant unobservable market parameters (Level 3)
Assets, Fair Value Disclosure [Abstract]
Total assets at fair value		62,436	61,964
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other real estate owned		27,182	29,487
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	$ 35,254	$ 32,477

[1] Amount is net of valuation allowance of $3.3 million at December 31, 2019 as required by ASC 310-10, "Receivables."