Business Combinations - Summary of Consideration Paid and Fair Value of Identifiable Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Oct. 09, 2015	Mar. 02, 2015	Jun. 30, 2016	Dec. 31, 2015
Liabilities assumed:
Goodwill resulting from acquisition of Alliance			$ 84,852	$ 85,212
Alliance Bancorp, Inc. [Member]
Liabilities assumed:
Goodwill resulting from acquisition of Alliance			$ 36,065	$ 36,425
Pennsylvania [Member] | Alliance Bancorp, Inc. [Member]
Consideration Paid:
Common shares issued (2,459,120)	$ 71,345
Cash paid to Alliance stockholders	26,576	$ 26,600
Value of consideration	97,921
Assets acquired:
Cash and due from banks	67,439
Investment securities	3,002
Loans	307,695
Premises and equipment	2,685
Deferred income taxes	7,669
Bank owned life insurance	12,923
Core deposit intangible	2,635
Other real estate owned	768
Other assets	3,641
Total assets	408,457
Liabilities assumed:
Deposits	341,682
Other Borrowings	2,826
Other liabilities	2,093
Total liabilities	346,601
Net assets acquired	61,856
Goodwill resulting from acquisition of Alliance	$ 36,065