Investment Securities - Schedule of Proceeds from Sales or Calls and Realized Gain and Losses of Available-for-sale Investment Securities and Other Securities (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Schedule of Available-for-sale Securities [Line Items]
Proceeds from sales of available-for-sale securities	$ 30,801	$ 26,319	$ 107,451	$ 196,584
Proceeds from calls of available-for-sale securities			721,414	401,579
Total	270,799	187,727	471,760	409,586
Realized gains on sales of available-for-sale securities	1,491	316	3,151	2,797
Realized losses on sales of available-for-sale securities	(1)	(22)	(447)	(47)
Other securities gains (losses)	241	18	(24)	80
Net securities gains	1,856	512	2,962	3,195
Calls [Member]
Schedule of Available-for-sale Securities [Line Items]
Proceeds from calls of available-for-sale securities	239,998	161,408	364,309	213,002
Realized gains on calls of available-for-sale securities	126	212	370	380
Realized losses on calls of available-for-sale securities	$ (1)	$ (12)	$ (88)	$ (15)