Business Combinations - Summary of Consideration Paid and Fair Value of Identifiable Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Sep. 05, 2014	Nov. 25, 2013	Jun. 30, 2015	Dec. 31, 2014
Consideration Paid:
Common shares issued (1,357,983)	$ 32,908
Cash paid to FNBW stockholders	32,028
Value of consideration	64,936
Assets acquired:
Cash and due from banks	40,605
Investment securities	41,822
Loans	175,578
Premises and equipment	1,611
Deferred income taxes	3,139
Bank owned life insurance	12,576
Core deposit intangible	3,240
Other Real Estate Owned	1,593
Other assets	4,952
Total assets	285,116
Liabilities assumed:
Deposits	228,844
FHLB advances	5,052
Other liabilities	2,990
Total liabilities	236,886
Net assets acquired:	48,230
Goodwill resulting from acquisition of FNBW			$ 48,987	$ 48,651
First Wyoming Financial Corporation [Member]
Consideration Paid:
Cash paid to FNBW stockholders		$ 32,000
Liabilities assumed:
Goodwill resulting from acquisition of FNBW	$ 16,706		$ 16,706	$ 16,370