Summary of Significant Accounting Policies (Details)				3 Months Ended												12 Months Ended
	Jul. 02, 2019 USD ($)	Jan. 01, 2019 USD ($)	Mar. 01, 2016 USD ($)	Dec. 31, 2019 USD ($) $ / shares	Sep. 30, 2019 $ / shares	Jun. 30, 2019 $ / shares	Mar. 31, 2019 USD ($) $ / shares	Dec. 31, 2018 USD ($) $ / shares	Sep. 30, 2018 $ / shares	Jun. 30, 2018 $ / shares	Mar. 31, 2018 $ / shares	Dec. 31, 2017 $ / shares shares	Sep. 30, 2017 $ / shares	Jun. 30, 2017 $ / shares	Mar. 31, 2017 $ / shares	Dec. 31, 2019 USD ($) $ / shares shares		Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 shares	Dec. 31, 2019 USD ($) market shares	Dec. 31, 2018 USD ($) shares
Accounting Policies [Abstract]
Number of Markets in Which Entity Operates | market																					12
Goodwill [Roll Forward]
Balance at December 31, 2018		$ 1,807,121,000					$ 1,807,121,000									$ 1,807,121,000
Goodwill, Acquired During Period																12,690,000
Balance at December 31, 2019				$ 1,819,811,000				$ 1,807,121,000								1,819,811,000		$ 1,807,121,000
Finite-lived Intangible Assets [Roll Forward]
Balance at December 31, 2017		46,161,000					46,161,000									46,161,000
Acquisitions																14,877,000
Amortization																(9,908,000)		(10,549,000)	$ (8,816,000)
Balance at December 31, 2018				51,130,000				46,161,000								51,130,000		46,161,000
Balance at December 31, 2018		1,853,282,000					1,853,282,000									1,853,282,000
Acquisitions																27,567,000
Amortization																(9,908,000)
Balance at December 31, 2019				1,870,941,000				1,853,282,000								1,870,941,000		1,853,282,000
Finite-Lived Intangible Assets, Net [Abstract]
Finite-Lived Intangible Assets, Gross																					$ 107,665,000	$ 92,787,000
Accumulated amortization																					(56,535,000)	(46,626,000)
Net book value		46,161,000		$ 51,130,000			$ 46,161,000	$ 46,161,000								$ 51,130,000		46,161,000			$ 51,130,000	46,161,000
Cash Equivalents and Cash Flows [Abstract]
Cash equivalents maturity period																90 days
Cash Payments [Abstract]
Interest																$ 287,272,000		199,464,000	91,628,000
Income taxes paid																86,960,000		55,626,000	81,539,000
Noncash Transactions [Abstract]
Loans charged-off to the allowance for loan losses																(28,467,000)		(30,400,000)	(22,046,000)
Real Estate Owned, Transfer to Real Estate Owned																17,937,000		3,524,000	6,228,000
Loans foreclosed upon with repossessions transferred to other repossessed assets																93,000		1,899,000	646,000
Other Real Estate Sales Financed																871,000		891,000	908,000
Fixed assets transferred to other real estate																8,182,000		0	0
Available-for-sale securities transferred to Held-to-Maturity																0		179,763,000	0
Held-for-sale loans transferred to held-for-investment loan portfolios																0		44,980,000	0
Common stock issued in connection with acquisitions																0		0	1,850,968,000
Right of Use Assets Recognized																$ 90,927,000	[1]	0	0
Loans [Abstract]
Number of loan segments																5
Net deferred loan fees																$ 13,700,000		7,400,000
Percentage of loan portfolio assigned specific risk rating																					80.30%
Other Assets [Abstract]
Premises and equipment, net																					$ 273,932,000	265,560,000
Amortization																2,700,000		3,000,000.0	2,500,000
Cash surrender value of life insurance																					652,700,000	525,700,000
Noninterest income related to cash surrender value of bank owned life insurance policies																17,400,000		12,500,000	7,900,000
investments are included in CRA investments																					58,400,000	32,800,000
Investments as per community reinvestment act																					100,900,000	72,600,000
Variable Interest Entity [Line Items]
Federal Reserve Bank and Federal Home Loan Bank (FHLB) stock																					80,400,000	70,200,000
Other Investments																					$ 38,200,000	26,400,000
Gain (loss) due to change in fair value of investments																2,800,000		2,700,000
Number of trusts investment																					12
Value of investments with trust companies																					$ 278,037,000	239,237,000
Other Real Estate Owned [Abstract]
Other real estate owned																					30,300,000	16,200,000
Valuation allowance related to other real estate owned																					772,000	1,000,000.0
Foreclosed real estate expense																4,200,000		723,000	1,100,000
Income Tax [Abstract]
Revaluation of deferred tax assets and liabilities																$ 0		$ 0	$ 31,486,000
Income Tax Contingency [Line Items]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued																					$ 0	$ 0
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options outstanding (in shares) | shares												276,468							276,468	552,372	119,274	178,591
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements | shares																399,600		338,545	567,611
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | shares																160,492		253,193	0
Basic earnings per share calculation [Abstract]
Numerator - Net income (loss) available to common stockholders																$ 400,881,000		$ 359,440,000	$ 173,979,000
Denominator - Weighted average common shares outstanding (in shares) | shares																76,364,303		77,111,372	63,760,578
Basic net income per common share (in dollars per share) | $ / shares				$ 1.26	$ 1.45	$ 1.31	$ 1.22	$ 1.24	$ 1.22	$ 1.13	$ 1.08	$ 0.35	$ 0.84	$ 0.81	$ 0.83	$ 5.25		$ 4.66	$ 2.73
Diluted net income per share calculation [Abstract]
Numerator - Net income (loss) available to common stockholders																$ 400,881,000		$ 359,440,000	$ 173,979,000
Denominator - Weighted average common shares outstanding (in shares) | shares																76,364,303		77,111,372	63,760,578
Dilutive shares (in shares) | shares																399,600		338,545	567,611
Weighted average diluted common shares outstanding (in shares) | shares																76,763,903		77,449,917	64,328,189
Diluted net income per common share (in dollars per share) | $ / shares				$ 1.26	$ 1.44	$ 1.31	$ 1.22	$ 1.23	$ 1.21	$ 1.12	$ 1.08	$ 0.35	$ 0.83	$ 0.80	$ 0.82	$ 5.22		$ 4.64	$ 2.70
New Accounting Pronouncements or Change in Accounting Principle
Right of Use Assets Recognized																$ 90,927,000	[1]	$ 0	$ 0
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount																			31,500,000
Variable Interest Entity, Primary Beneficiary
Variable Interest Entity [Line Items]
Value of investments with trust companies																					$ 4,000,000.0
Small Impaired Loans
Financing Receivable, Impaired [Line Items]
Principal balance of loans subject to individual determination of impairment																					1,000,000.0
Premises and Equipment | Minimum
Premises and Equipment and Leaseholds [Abstract]
Premises and equipment, useful life																3 years
Premises and Equipment | Maximum
Premises and Equipment and Leaseholds [Abstract]
Premises and equipment, useful life																30 years
Computer Software, Intangible Asset
Other Assets [Abstract]
Premises and equipment, net																					$ 6,000,000.0	$ 7,700,000
Computer Software, Intangible Asset | Minimum
Premises and Equipment and Leaseholds [Abstract]
Premises and equipment, useful life																3 years
Computer Software, Intangible Asset | Maximum
Premises and Equipment and Leaseholds [Abstract]
Premises and equipment, useful life																7 years
Bankers Healthcare Group, LLC
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage																					49.00%
Business Acquisition [Line Items]
Cash paid to redeem common stock			$ 74,100,000
Finite-lived Intangible Assets [Roll Forward]
Amortization																$ (1,900,000)		$ (2,800,000)	$ (3,300,000)
Internal Revenue Service (IRS) | Minimum
Income Tax Contingency [Line Items]
Tax year open to audit under the statute of limitation																				2016
Internal Revenue Service (IRS) | Maximum
Income Tax Contingency [Line Items]
Tax year open to audit under the statute of limitation																2019
Advocate Capital
Business Acquisition [Line Items]
Cash paid to redeem common stock	$ 59,000,000.0
Borrowings	134,300,000
Loans, net of allowance for loan losses	$ 45,600,000
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock options outstanding (in shares) | shares																					119,274
Accounting Standards Update 2016-02
Noncash Transactions [Abstract]
Right of Use Assets Recognized		79,900,000
New Accounting Pronouncements or Change in Accounting Principle
Right of Use Assets Recognized		$ 79,900,000

[1] Includes $79.9 million recognized upon initial adoption of ASU 2016-02 on January 1, 2019.