Fair Value of Financial Instruments - Summary of Significant Unobservable Inputs Used in Fair Value Measurement of Level 3 Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified															9 Months Ended				9 Months Ended						9 Months Ended	12 Months Ended			12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended	9 Months Ended					12 Months Ended							9 Months Ended					12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Sep. 30, 2014 Other Real Estate Owned [Member]	Dec. 31, 2013 Other Real Estate Owned [Member]	Sep. 30, 2013 Other Real Estate Owned [Member]	Sep. 30, 2014 Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Covered Other Real Estate Owned [Member]	Sep. 30, 2013 Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Purchased Non-Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Purchased Non-Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member]	Dec. 31, 2013 Level 3 [Member]	Sep. 30, 2013 Level 3 [Member]	Sep. 30, 2014 Level 3 [Member] Impaired Loans Carried at Fair Value [Member]	Sep. 30, 2014 Level 3 [Member] Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Other Real Estate Owned [Member]	Sep. 30, 2013 Level 3 [Member] Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Purchased Non-Covered Loans [Member]	Sep. 30, 2014 Level 3 [Member] Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Covered Other Real Estate Owned [Member]	Sep. 30, 2013 Level 3 [Member] Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Purchased Non-Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Purchased Non-Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Fair Value Measurement, Recurring [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value Measurement, Recurring [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Impaired Loans Carried at Fair Value [Member]	Sep. 30, 2014 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Impaired Loans Carried at Fair Value [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Purchased Non-Covered Loans [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Purchased Non-Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Purchased Non-Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Fair Value Measurement, Nonrecurring [Member] Covered Loans [Member]	Sep. 30, 2014 Level 3 [Member] Minimum [Member] Impaired Loans Carried at Fair Value [Member]	Sep. 30, 2014 Level 3 [Member] Minimum [Member] Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Minimum [Member] Purchased Non-Covered Loans [Member]	Sep. 30, 2014 Level 3 [Member] Minimum [Member] Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Minimum [Member] Fair Value Measurement, Recurring [Member]	Dec. 31, 2013 Level 3 [Member] Minimum [Member] Fair Value Measurement, Recurring [Member]	Dec. 31, 2013 Level 3 [Member] Minimum [Member] Fair Value Measurement, Nonrecurring [Member] Impaired Loans Carried at Fair Value [Member]	Dec. 31, 2013 Level 3 [Member] Minimum [Member] Fair Value Measurement, Nonrecurring [Member] Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Minimum [Member] Fair Value Measurement, Nonrecurring [Member] Purchased Non-Covered Loans [Member]	Dec. 31, 2013 Level 3 [Member] Minimum [Member] Fair Value Measurement, Nonrecurring [Member] Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Minimum [Member] Fair Value Measurement, Nonrecurring [Member] Purchased Non-Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Minimum [Member] Fair Value Measurement, Nonrecurring [Member] Covered Loans [Member]	Sep. 30, 2014 Level 3 [Member] Maximum [Member] Impaired Loans Carried at Fair Value [Member]	Sep. 30, 2014 Level 3 [Member] Maximum [Member] Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Maximum [Member] Purchased Non-Covered Loans [Member]	Sep. 30, 2014 Level 3 [Member] Maximum [Member] Covered Other Real Estate Owned [Member]	Sep. 30, 2014 Level 3 [Member] Maximum [Member] Fair Value Measurement, Recurring [Member]	Dec. 31, 2013 Level 3 [Member] Maximum [Member] Fair Value Measurement, Recurring [Member]	Dec. 31, 2013 Level 3 [Member] Maximum [Member] Fair Value Measurement, Nonrecurring [Member] Impaired Loans Carried at Fair Value [Member]	Dec. 31, 2013 Level 3 [Member] Maximum [Member] Fair Value Measurement, Nonrecurring [Member] Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Maximum [Member] Fair Value Measurement, Nonrecurring [Member] Purchased Non-Covered Loans [Member]	Dec. 31, 2013 Level 3 [Member] Maximum [Member] Fair Value Measurement, Nonrecurring [Member] Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Maximum [Member] Fair Value Measurement, Nonrecurring [Member] Purchased Non-Covered Other Real Estate Owned [Member]	Dec. 31, 2013 Level 3 [Member] Maximum [Member] Fair Value Measurement, Nonrecurring [Member] Covered Loans [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	$ 113,697	$ 126,066	$ 136,094	$ 35,320	$ 33,351	$ 39,978	$ 28,883	$ 45,893	$ 52,552	$ 13,660	$ 4,276	$ 113,697	$ 126,066	$ 136,094		$ 35,320	$ 33,351	$ 39,978		$ 28,883	$ 45,893	$ 52,552	$ 13,660	$ 4,276			$ 42,546	$ 35,834	$ 33,351	$ 35,320	$ 448,753	$ 45,893	$ 28,883	$ 4,276	$ 13,660	$ 390,237
Investment securities available for sale, Recurring	$ 641,863	$ 554,693	$ 384,388									$ 2,500	$ 2,000	$ 2,000											$ 2,500	$ 2,000
Valuation Technique															Third party appraisals and discounted cash flows	Third party appraisals			Third party appraisals	Third party appraisals					Discounted par values	Discounted par values	Third party appraisals and discounted cash flows		Third party appraisals		Third party appraisals and discounted cash flows	Third party appraisals		Third party appraisals		Third party appraisals and discounted cash flows
Fair value inputs discount rate range																																					(4.00%)	10.00%	22.00%	10.00%	0.00%	0.00%	4.00%	10.00%	1.00%	10.00%	15.00%	1.75%	90.00%	90.00%	94.00%	90.00%	0.00%	0.00%	75.00%	74.00%	40.00%	86.00%	63.00%	75.00%