Business Combinations - Schedule of Changes to Goodwill (Detail) $ in Thousands	12 Months Ended
Dec. 31, 2017 USD ($)
Goodwill [Roll Forward]
Goodwill, Beginning balance	$ 167,539
Goodwill, Ending balance	166,007
Penn Liberty
Goodwill [Roll Forward]
Goodwill, Beginning balance	68,814
Goodwill, Ending balance	67,226
Penn Liberty \| Deferred income taxes
Goodwill [Roll Forward]
Effect of adjustments	880
Penn Liberty \| Loans
Goodwill [Roll Forward]
Effect of adjustments	279
Penn Liberty \| Other assets
Goodwill [Roll Forward]
Effect of adjustments	(1,440)
Penn Liberty \| Other liabilities
Goodwill [Roll Forward]
Effect of adjustments	$ (1,307)

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant