Business Combinations - Additional Information (Detail)			1 Months Ended	3 Months Ended
	Oct. 09, 2015 USD ($) $ / shares shares	Mar. 02, 2015 USD ($) shares	Aug. 31, 2016 USD ($)	Mar. 31, 2016 USD ($) Branch	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Assets				$ 5,684,994,000	$ 5,585,962,000	$ 5,584,637,000
Loans				3,757,729,000		3,729,050,000
Deposits				4,068,771,000		4,016,566,000
Goodwill resulting from acquisition of FNBW				84,854,000	85,212,000	85,212,000
Alliance Bancorp, Inc. [Member]
Business Acquisition [Line Items]
Goodwill resulting from acquisition of FNBW				$ 36,067,000		36,425,000
Alliance Bancorp, Inc. [Member] | Pennsylvania [Member]
Business Acquisition [Line Items]
Transaction value, cash and stock	$ 97,921,000
Agreement date of merger				Mar. 02, 2015
Cash paid to Alliance stockholders	$ 26,576,000	$ 26,576,000
Common stock shares issued | shares	2,459,120	2,459,120
Effective date of merger				Oct. 09, 2015
Goodwill resulting from acquisition of FNBW	$ 36,067,000
Alliance Bancorp, Inc. [Member] | Pennsylvania [Member] | NASDAQ Stock Market [Member]
Business Acquisition [Line Items]
Closing share price | $ / shares	$ 29.01
Alliance Bancorp, Inc. [Member] | Pennsylvania [Member] | Core Deposits [Member]
Business Acquisition [Line Items]
Intangibles	$ 2,600,000
Amortized period	10 years
Alliance Bancorp, Inc. [Member] | Pennsylvania [Member] | Non-compete Covenants [Member]
Business Acquisition [Line Items]
Intangibles	$ 511,000
Alliance Bancorp, Inc. [Member] | Pennsylvania [Member] | Non-compete Covenants [Member] | Minimum [Member]
Business Acquisition [Line Items]
Amortized period	6 months
Alliance Bancorp, Inc. [Member] | Pennsylvania [Member] | Non-compete Covenants [Member] | Maximum [Member]
Business Acquisition [Line Items]
Amortized period	18 months
First Wyoming Financial Corporation [Member] | Acquisition Related Costs [Member]
Business Acquisition [Line Items]
Merger expenses				$ 426,000	$ 666,000
Penn Liberty Financial Corporation [Member] | Pennsylvania [Member]
Business Acquisition [Line Items]
Assets						704,000,000
Loans						510,000,000
Deposits						$ 621,000,000
Number of branch locations | Branch				11
Agreement date of merger				Nov. 23, 2015
Scenario, Forecast [Member] | Penn Liberty Financial Corporation [Member] | Pennsylvania [Member]
Business Acquisition [Line Items]
Transaction value, cash and stock			$ 101,000,000