Recent Developments Including Mergers and Acquisitions - Additional Information (Detail) - USD ($)	1 Months Ended			3 Months Ended							12 Months Ended
	Oct. 31, 2015	Jun. 30, 2015	Jan. 31, 2015	Dec. 31, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 08, 2015	Jan. 24, 2014
Business Combination Separately Recognized Transactions [Line Items]
Goodwill				$ 54,042,000			$ 44,962,000				$ 54,042,000	$ 44,962,000	$ 44,545,000
Gain on sale of securities	$ 2,100,000			$ 2,148,000	$ 5,392,000	$ 1,729,000	$ 822,000	$ 284,000	$ 85,000	$ 450,000	$ 9,269,000	$ 1,641,000	$ 420,000
Pretax gain on sale of investments		$ 5,200,000	$ 1,700,000
Bank of Commerce [Member]
Business Combination Separately Recognized Transactions [Line Items]
Total assets acquired														$ 196,000,000
Loans														147,000,000
Deposits														175,000,000
Equity capital														$ 22,000,000
Percentage of voting interests acquired														100.00%
Intangibles assets, net														$ 7,100,000
Goodwill														$ 9,400,000
The Bank of Union [Member] | BancFirst [Member]
Business Combination Separately Recognized Transactions [Line Items]
Loans															$ 121,000,000
Deposits															302,000,000
Equity capital															4,800,000
Intangibles assets, net															2,200,000
Goodwill															417,000
Other real estate															$ 10,000