Business Combinations - Summary of Consideration Paid and Fair Value of Identifiable Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Aug. 12, 2016	Sep. 30, 2017	Dec. 31, 2016
Liabilities assumed:
Goodwill resulting from acquisition of Penn Liberty		$ 166,007	$ 167,539
Penn Liberty Financial Corporation
Liabilities assumed:
Goodwill resulting from acquisition of Penn Liberty		$ 67,226	$ 68,814
Pennsylvania | Penn Liberty Financial Corporation
Consideration Transferred:
Common shares issued (1,806,748)	$ 68,352
Common shares issued (in shares)	1,806,748
Cash paid to Penn Liberty stock and option holders	$ 40,549
Value of consideration	108,901
Assets acquired:
Cash and due from banks	102,301
Investment securities	627
Loans	483,203
Premises and equipment	6,817
Deferred income taxes	6,542
Bank owned life insurance	8,666
Core deposit intangible	2,882
Other real estate owned	996
Other assets	12,085
Total assets	624,119
Liabilities assumed:
Deposits	568,706
Other borrowings	10,000
Other liabilities	3,738
Total liabilities	582,444
Net assets acquired:	41,675
Goodwill resulting from acquisition of Penn Liberty	$ 67,226