Business Combinations - Schedule of Changes in Accretable Discounts Related Acquired Non-Covered Loans (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Schedule Of Covered Loans Acquired Accretable Discounts [Line Items]
Balance, beginning of year	$ 15,578	$ 25,493	$ 25,493
Accretion	(6,251)	(15,432)	(22,188)
Transfers between non-accretable and accretable discounts, net	2,817	5,850	12,273
Balance, end of year	12,060	15,911	15,578
Non-Covered Loans [Member]
Schedule Of Covered Loans Acquired Accretable Discounts [Line Items]
Balance, beginning of year	674,239	448,753	448,753
Additions due to acquisitions	195,818	279,441	279,441
Accretion	(5,388)	(3,635)	(9,745)
Balance, end of year	808,313	702,131	674,239
Non-Covered Loans [Member] | Discount Accretion [Member]
Schedule Of Covered Loans Acquired Accretable Discounts [Line Items]
Balance, beginning of year	25,716	26,189	26,189
Additions due to acquisitions	4,686	7,799	7,799
Accretion	(5,388)	(3,635)	(9,745)
Accretable discounts removed due to charge-offs	(1,685)
Transfers between non-accretable and accretable discounts, net	(1,007)	1,968	1,473
Balance, end of year	$ 22,322	$ 32,321	$ 25,716