Summary of Accounting Policies - Additional Information (Details) - USD ($)				3 Months Ended		12 Months Ended
	Jun. 01, 2018	May 31, 2018	Jan. 01, 2018	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019	Oct. 31, 2018
Significant Of Accounting Policies [Line Items]
Investment securities held-to-maturity (estimated fair value of $311 at December 31, 2017)				$ 0		$ 0	$ 290,000
Trading Securities				0		0	0
Reserve for unfunded commitments, Amount				600,000		600,000	800,000
Loan in process of foreclosure				3,800,000		3,800,000	4,400,000
Residential real estate properties held				2,406,000		2,406,000	7,605,000
Goodwill impairment						0	0	$ 0
Expense under cash based long term incentive plan						$ 6,000,000	7,300,000	4,400,000
ASU 2016-01
Significant Of Accounting Policies [Line Items]
Adjustment to retained earnings			$ 1,000,000
ASU 2016-02 | Subsequent Event
Significant Of Accounting Policies [Line Items]
Right-of-use asset									$ 65,900,000
2018 Employee Stock Purchase Plan | Common Class A
Significant Of Accounting Policies [Line Items]
Percentage of discount on fair market value of common stock	15.00%					15.00%
Executives And Senior Officers
Significant Of Accounting Policies [Line Items]
Percentage of base deferred compensation						25.00%
Percentage of incentive compensation						100.00%
Employee Contribution						$ 0	0	$ 0
401 K Plan
Significant Of Accounting Policies [Line Items]
Retained earning contribution						100.00%
Employer match 100% up to 3% Of Employee Compensation | 401 K Plan
Significant Of Accounting Policies [Line Items]
Defined contribution plan percentage						100.00%
Employer match 50% Between 3% to 5% Of Employee Compensation | 401 K Plan
Significant Of Accounting Policies [Line Items]
Defined contribution plan percentage						50.00%
Employee contribution percentage						3.00%
Maximum
Significant Of Accounting Policies [Line Items]
Share repurchase program authorized amount				81,000,000		$ 81,000,000				$ 50,000,000
Federal funds sold periods						7 days
Maximum | Employer match 100% up to 3% Of Employee Compensation | 401 K Plan
Significant Of Accounting Policies [Line Items]
Employee contribution percentage						3.00%
Minimum
Significant Of Accounting Policies [Line Items]
Federal funds sold periods						1 day
Variable Interest Entity, Not Primary Beneficiary
Significant Of Accounting Policies [Line Items]
Proceeds from sale of previously owned net profit interest				5,300,000
Net Profits interest				5,800,000		$ 5,800,000	15,800,000
OREO
Significant Of Accounting Policies [Line Items]
Residential real estate properties held				$ 900,000		$ 900,000	$ 2,700,000
Unrelated Third Party | Town & Country Insurance Agency, Inc.
Significant Of Accounting Policies [Line Items]
Sale of net assets		$ 11,100,000
Unrelated Third Party | Town & Country Insurance Agency, Inc. | Noninterest Income
Significant Of Accounting Policies [Line Items]
Sale of assets, pre-tax gain					$ 4,900,000
Unrelated Third Party | Town & Country Insurance Agency, Inc. | Noninterest expenses
Significant Of Accounting Policies [Line Items]
Sale related expenses					$ 1,100,000
Unrelated Third Party | Town & Country Insurance Agency, Inc. | Goodwill and Intangible Assets
Significant Of Accounting Policies [Line Items]
Sale of net assets		$ 10,900,000