Employee Benefit Plans - Additional Information (Details)				12 Months Ended
	Dec. 31, 2019	Jun. 28, 2016	Dec. 31, 2014 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum percentage of amount to be contributed by the employer				6.00%
Matching and profit sharing vesting period				5 years
Contribution provided by the bank to the plan				$ 1,379,000	$ 1,290,000	$ 922,000
Discretionary contribution percentage				25.00%	25.00%	25.00%
Post retirement benefits payable				$ 2,023,000	$ 1,914,000
Expense related to plans				30,000	313,000	$ 314,000
Payments to participants				205,000	202,000	205,000
Cash surrender value on bank owned life insurance				10,556,000	10,331,000
Cash value income				$ 181,000	136,000	92,000
Description of stock split				the Company declared a 100-for-1 stock split, increasing the number of issued and authorized shares from 171,800 to 17,180,000 and 250,000 to 25,000,000, respectively.
Stock split ratio		0.01
Deferred compensation				$ 6,710,000	12,343,000
Salaries, commissions and employee benefits				113,992,000	84,214,000	63,863,000
Deferred Compensation Plans and Agreements
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Payments to participants				$ 1,601,000	2,614,000
Description of stock split				100-for-one stock split
Stock split ratio				100
Other liabilities				$ 3,758,000	9,452,000
Accrued compensation reclassified to additional paid in capital				$ 5,388
Number of units remaining in equity based incentive plan for cash settlement | shares				180,447
Salaries, commissions and employee benefits				$ 5,073,000	$ 2,921,000
Deferred Compensation Plans and Agreements | Chief Executive Officer
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
IPO price | $ / shares				$ 19.00
Deferred compensation			$ 3,000,000			$ 3,000,000
Deferred compensation payment date			Dec. 31, 2019
Deferred stock units issued | shares				157,895
Deferred Compensation Plans and Agreements | Chief Executive Officer | Scenario, Forecast
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Deferred stock units conversion basis	1-for-1
Deferred Compensation Plans and Agreements | 2010 EBI Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation award vesting period				5 years
Employee retirement age under EBI plan				65 years
Valuation of unit by percentage of assets				7.50%
Share-based compensation terms of award, description				Pursuant to the terms of the 2010 EBI Plan, each EBI Unit vests ratably over five years, or earlier upon a change of control, death or disability or retirement after age 65. On or shortly following the vesting date, the holder of an EBI Unit will receive an amount in cash (or, if so elected by the participant following the IPO, in stock) equal to the fair market value of a share of common stock on the December 31 immediately preceding the payment date. Prior to the IPO, fair market value was determined by dividing 7.5% of the total assets of the Bank by the total number of outstanding common stock shares of the Company. Following the IPO, EBI Units are valued based upon the Company’s stock price. Units under this plan became fully vested January, 2017.
Deferred Compensation Plans and Agreements | Preferred EBI Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation terms of award, description				The Preferred EBI Plan has the same terms and conditions as those described above for the 2010 EBI Plan, with the exception of a seven year ratable vesting period. Units under this plan became fully vested January, 2017.
Deferred Compensation Plans and Agreements | 2012 EBI Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation award vesting period				3 years
Employee retirement age under EBI plan				65 years
Share-based compensation terms of award, description				Pursuant to the terms of the 2012 EBI Plan, each EBI Unit vests and becomes payable following the third anniversary of the date of grant, or earlier upon a change of control, death or disability or retirement after age 65. On or shortly following the vesting date, the holder of an EBI Unit will receive an amount in cash (or, if so elected by the participant following the IPO, in stock) equal to the fair market value of a share of common stock on the December 31 immediately preceding the payment date. Following the IPO, EBI Units are valued based upon the Company’s stock price. Prior to the IPO, fair market value of the Company was determined based upon the average of the sum of (a) 15 times the Company’s after-tax earnings, based on a default tax rate imposed by the Code, and (b) 1.5 times the Company’s tangible book value, defined as the consolidated equity of the Company less unrealized gains (losses) and less goodwill and intangible assets. Following the IPO, EBI Units outstanding under the 2012 EBI Plan were adjusted to prevent dilution of these EBI Units as a result of the IPO pursuant to the following conversion formula: (i) the number of EBI Units outstanding under the 2012 EBI Plan (as adjusted for the stock split), multiplied by (ii) 1.13 (determined by dividing $21.4085, the fair market value per EBI Unit as determined under the 2012 EBI Plan, by $19.00, the IPO price).
Fair market value per EBI | $ / shares				$ 21.4085
IPO price | $ / shares				$ 19.00