Mergers and Acquisitions - Estimated Fair Value of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 16, 2015	Dec. 31, 2017	Dec. 31, 2016	Sep. 14, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Equity interest issued		$ 0	$ 0		$ 110,551
Goodwill		$ 94,697	$ 94,697		$ 95,657
Share Price				$ 31.75
SBM Financial, Inc. [Member]
Business Acquisition [Line Items]
Cash	$ 26,125
Equity interest issued	108,561
Total consideration paid	136,676
Loans and loans held for sale	628,030
Cash and due from banks	86,042
Investments	39,742
Deferred tax assets	25,782
Premises and equipment	23,944
OREO	729
Core deposit intangible assets	6,608
Other assets	5,408
Deposits and borrowings	721,186
Other liabilities	8,314
Total identified assets acquired and liabilities assumed, at fair value	86,785
Goodwill	$ 49,891
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares	4,124,643
Share Price	$ 26.32
Nonqualified Stock Options [Member] | SBM Financial, Inc. [Member]
Business Acquisition [Line Items]
Equity interest issued	$ 1,990
Predecessor [Member] | SBM Financial, Inc. [Member]
Business Acquisition [Line Items]
Loans and loans held for sale	639,390
Cash and due from banks	86,042
Investments	39,716
Deferred tax assets	26,293
Premises and equipment	16,851
OREO	2,530
Core deposit intangible assets	0
Other assets	5,421
Deposits and borrowings	719,640
Other liabilities	8,512
Total identified assets acquired and liabilities assumed, at fair value	88,091
Scenario, Adjustment [Member] | SBM Financial, Inc. [Member]
Business Acquisition [Line Items]
Loans and loans held for sale	137
Cash and due from banks	0
Investments	0
Deferred tax assets	666
Premises and equipment	0
OREO	0
Core deposit intangible assets	0
Other assets	157
Deposits and borrowings	0
Other liabilities	0
Total identified assets acquired and liabilities assumed, at fair value	960
Estimate of Fair Value Measurement [Member] | Scenario, Adjustment [Member] | SBM Financial, Inc. [Member]
Business Acquisition [Line Items]
Loans and loans held for sale	(11,497)
Cash and due from banks	0
Investments	26
Deferred tax assets	(1,177)
Premises and equipment	7,093
OREO	(1,801)
Core deposit intangible assets	6,608
Other assets	(170)
Deposits and borrowings	1,546
Other liabilities	(198)
Total identified assets acquired and liabilities assumed, at fair value	$ (2,266)