Loans - Schedule of Carrying Amount of Acquired Covered Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014		Sep. 30, 2014
Accounts, Notes, Loans and Financing Receivable
Total covered loans	$ 253,541	$ 444,544
Covered Loans
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	52,301	37,532
Acquired performing loans	201,240	407,012
Total covered loans	253,541	444,544	[1]	$ 524,189
Covered Loans | Commercial Loans
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	19,143	1,253
Acquired performing loans	35,866	219,133
Total covered loans	55,009	220,386	[1]
Covered Loans | Commercial Loans | Real Estate
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	18,576	1,253
Acquired performing loans	25,014	187,873
Total covered loans	43,590	189,126	[1]	247,156
Covered Loans | Commercial Loans | Commercial and Industrial
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	567	0
Acquired performing loans	10,852	31,260
Total covered loans	11,419	31,260	[1]	34,234
Covered Loans | Residential Mortgage Loans
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	25,100	22,918
Acquired performing loans	94,826	105,106
Total covered loans	119,926	128,024	[1]	130,976
Covered Loans | Residential Mortgage Loans | Residential 1-4 Family
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	25,100	22,918
Acquired performing loans	94,826	105,106
Total covered loans	119,926	128,024	[1]
Covered Loans | Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	8,058	13,361
Acquired performing loans	70,548	82,773
Total covered loans	78,606	96,134	[1]	$ 111,823
Covered Loans | Consumer and Other Loans | Home Equity
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	8,038	12,872
Acquired performing loans	69,188	79,558
Total covered loans	77,226	92,430	[1]
Covered Loans | Consumer and Other Loans | Other
Accounts, Notes, Loans and Financing Receivable
Acquired impaired loans	20	489
Acquired performing loans	1,360	3,215
Total covered loans	$ 1,380	$ 3,704	[1]

[1] Included as covered loans at December 31, 2014 is $174.7 million of assets whose reimbursable loss periods ended as of January 1, 2015.