Fair Value of Financial Instruments (Details) - USD ($) $ in Thousands		Sep. 30, 2020	Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Valuation allowance		$ 10,700	$ 3,280
Recurring
Assets, Fair Value Disclosure [Abstract]
U.S. Treasury securities		84,464	72,867
U.S. government agency securities		76,859	79,692
Mortgage-backed securities		1,701,212	1,463,907
State and municipal securities		1,327,721	1,714,453
Agency-backed securities		168,839	152,972
Corporate notes and other		104,327	56,104
Total investment securities available-for-sale		3,463,422	3,539,995
Other Investments		66,872	63,291
Other assets		265,835	134,040
Total assets at fair value		3,796,129	3,737,326
Liabilities at fair value: [Abstract]
Other liabilities		198,724	87,613
Total liabilities at fair value		198,724	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		84,464	72,867
U.S. government agency securities		76,859	79,692
Mortgage-backed securities		1,701,212	1,463,907
State and municipal securities		1,312,248	1,698,550
Agency-backed securities		168,839	152,972
Corporate notes and other		104,327	56,104
Total investment securities available-for-sale		3,447,949	3,524,092
Other Investments		25,666	25,135
Other assets		265,835	134,040
Total assets at fair value		3,739,450	3,683,267
Liabilities at fair value: [Abstract]
Other liabilities		198,724	87,613
Total liabilities at fair value		198,724	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		15,473	15,903
Agency-backed securities		0	0
Corporate notes and other		0	0
Total investment securities available-for-sale		15,473	15,903
Other Investments		41,206	38,156
Other assets		0	0
Total assets at fair value		56,679	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		97,243	61,965
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other real estate owned		19,445	29,487
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	77,798	32,478
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		97,243	61,965
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Abstract]
Other real estate owned		19,445	29,487
Impaired Financing Receivable, with Related Allowance, Recorded Investment	[1]	$ 77,798	$ 32,478

[1] The carrying value of collateral dependent loans at September 30, 2020 is net of a valuation allowance of $10.7 million, and the carrying value of impaired loans at December 31, 2019 is net of a valuation allowance of $3.3 million