Basis of Presentation - Additional Information (Details) $ / shares in Units, $ in Thousands						3 Months Ended		6 Months Ended
	May 26, 2017 USD ($) $ / shares shares	Jan. 02, 2017 USD ($)	Sep. 15, 2016 USD ($) $ / shares shares	Aug. 15, 2016 USD ($)	Jun. 28, 2016 shares	Jun. 30, 2017 $ / shares shares	Jun. 30, 2016 shares	Jun. 30, 2017 USD ($) Branch $ / shares shares	Jun. 30, 2016 shares	Jul. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	Jul. 31, 2016 shares
Class Of Stock [Line Items]
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
Common stock, shares issued						28,968,160		28,968,160			24,107,660
Common stock, shares authorized						75,000,000		75,000,000			75,000,000
Proceeds from issuance of common stock, net of offering costs | $								$ 152,721
Common stock sold and issued, par value | $ / shares						$ 1		$ 1			$ 1
Short-term borrowings | $											$ 150,000
Dilutive instruments outstanding						559,490	0	505,786	0
ASC 860-50-35, Transfers and Servicing
Class Of Stock [Line Items]
Adjustment to retained earnings | $		$ 615
Federal Home Loan Bank Advances | Subsequent Event
Class Of Stock [Line Items]
Short-term borrowings | $										$ 100,000
Pro forma
Class Of Stock [Line Items]
Effective tax rate							37.45%		37.39%
Initial Public Offering
Class Of Stock [Line Items]
Common stock sold and issued, shares			6,764,704
Common stock sold and issued, price per share | $ / shares			$ 19
Proceeds from issuance of common stock, net of offering costs | $			$ 115,525
Distribution to majority shareholder from net proceeds | $			55,000
Repayments of aggregate principal amount of subordinated notes from net proceeds | $			$ 10,075	$ 10,075
Private Placement
Class Of Stock [Line Items]
Common stock sold and issued, shares	4,806,710
Proceeds from issuance of common stock, net of offering costs | $	$ 152,700
Common stock sold and issued, par value | $ / shares	$ 1.00
Common stock purchase price per share | $ / shares	$ 33.00
Minimum
Class Of Stock [Line Items]
Common stock, shares issued					171,800
Common stock, shares authorized					250,000							25,000,000
Maximum
Class Of Stock [Line Items]
Common stock, shares issued					17,180,000
Common stock, shares authorized					25,000,000							75,000,000
FirstBank
Class Of Stock [Line Items]
Number of bank branches | Branch								45