Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($) $ in Thousands		12 Months Ended
	Sep. 09, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Intangible Assets Goodwill And Other Assets [Line Items]
Goodwill		$ 573,800	$ 480,600
Other intangible assets		19,384	10,336
Amortization of intangible assets		2,900	2,400	$ 1,900
Amortization of intangible assets		3,598	3,136	$ 1,920
Amortization expense expected to be recognized in year one		4,066
Amortization expense expected to be recognized in year two		3,543
Amortization expense expected to be recognized in year three		3,037
Your Community Bankshares, Inc [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Goodwill acquired	$ 92,889	92,900
Your Community Bankshares, Inc [Member] | Core Deposits [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Intangible assets acquired		12,000
ESB Financial Corporation [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Goodwill acquired		168,800
ESB Financial Corporation [Member] | Core Deposits [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Intangible assets acquired		5,300
YCB and ESB [Member] | Noncompete Agreements [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Amortization of intangible assets		700	$ 700
Amortization expense expected to be recognized in year one		900
Amortization expense expected to be recognized in year two		600
Amortization expense expected to be recognized in year three		$ 200
Minimum [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Intangible asset, useful life		10 years
Minimum [Member] | YCB and ESB [Member] | Noncompete Agreements [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Intangible asset, useful life		1 year
Maximum [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Intangible asset, useful life		16 years
Maximum [Member] | YCB and ESB [Member] | Noncompete Agreements [Member]
Intangible Assets Goodwill And Other Assets [Line Items]
Intangible asset, useful life		4 years