Business Combinations - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended
	Dec. 23, 2013 Prosperity Bank [Member] Location	Dec. 23, 2013 Prosperity Banking Company [Member]	Jun. 30, 2014 Coastal Bank [Member] Location	Jun. 30, 2014 Coastal Bankshares, Inc. [Member]	Jun. 30, 2014 Coastal Bankshares, Inc. [Member] Warrant [Member]
Business Acquisition [Line Items]
Number of banking locations	12		6
Shares to receive for each share of Prosperity common stock pursuant to the merger agreement		3.125		0.4671
Issuance of common stock, shares		1,168,918		1,598,987
Issuance of common stock, fair value		$ 24.6		$ 34.5
Cash in exchange for outstanding warrants					$ 2.8
Cash to receive for each share of Prosperity common stock pursuant to the merger agreement		$ 41.50