Premises and Equipment, Net - Additional Information (Details)	12 Months Ended
Dec. 31, 2017 USD ($) Branch	Dec. 31, 2016 USD ($) Branch Land	Dec. 31, 2015 USD ($)
Property Plant And Equipment [Abstract]
Number of branches held for sale \| Branch	3	5
Number of land held for sale \| Land		2
Property valuation adjustments	$ 338,000	$ 750,000	$ 0
Premises and Equipment, Net, by Type [Abstract]
Depreciation and amortization of premises and equipment	$ 14,300,000	$ 13,200,000	$ 14,000,000

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration