Investment Securities - Summary of Continuous Unrealized Loss Position of Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	$ 615,765	$ 43,813
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	2,844	55
Fair Value, 12 Months or Longer, Available-for-sale	5,961	509,509
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	1	12,123
Fair Value, Available-for-sale	621,726	553,322
Gross Unrealized Holding Losses, Available-for-sale	2,845	12,178
Fair Value, Less Than 12 Months, Held-to-maturity	425,374
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(2,746)
Fair Value, 12 Months or Longer, Held-to-maturity	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0
Fair Value, Held-to-maturity	425,374
Gross Unrealized Holding Losses, Held-to-maturity	(2,746)
CMO's/REMIC's - Residential [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	171,923	0
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	1,074	0
Fair Value, 12 Months or Longer, Available-for-sale	0	31,143
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	0	277
Fair Value, Available-for-sale	171,923	31,143
Gross Unrealized Holding Losses, Available-for-sale	1,074	277
Fair Value, Less Than 12 Months, Held-to-maturity	0
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	0
Fair Value, 12 Months or Longer, Held-to-maturity	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0
Fair Value, Held-to-maturity	0
Gross Unrealized Holding Losses, Held-to-maturity	0
Government Agency/GSEs [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	5,745	22,224
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	7	28
Fair Value, 12 Months or Longer, Available-for-sale	0	307,873
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	0	8,200
Fair Value, Available-for-sale	5,745	330,097
Gross Unrealized Holding Losses, Available-for-sale	7	8,228
Fair Value, Less Than 12 Months, Held-to-maturity	84,495
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(734)
Fair Value, 12 Months or Longer, Held-to-maturity	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0
Fair Value, Held-to-maturity	84,495
Gross Unrealized Holding Losses, Held-to-maturity	(734)
Residential Mortgage-backed Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	437,699	19,636
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	1,761	4
Fair Value, 12 Months or Longer, Available-for-sale	0	145,681
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	0	3,024
Fair Value, Available-for-sale	437,699	165,317
Gross Unrealized Holding Losses, Available-for-sale	1,761	3,028
Fair Value, Less Than 12 Months, Held-to-maturity	230,760
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(1,293)
Fair Value, 12 Months or Longer, Held-to-maturity	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0
Fair Value, Held-to-maturity	230,760
Gross Unrealized Holding Losses, Held-to-maturity	(1,293)
Municipal Bonds [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	398	1,953
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	2	23
Fair Value, 12 Months or Longer, Available-for-sale	5,961	24,812
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	1	622
Fair Value, Available-for-sale	6,359	26,765
Gross Unrealized Holding Losses, Available-for-sale	3	645
Fair Value, Less Than 12 Months, Held-to-maturity	110,119
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(719)
Fair Value, 12 Months or Longer, Held-to-maturity	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0
Fair Value, Held-to-maturity	110,119
Gross Unrealized Holding Losses, Held-to-maturity	(719)
Other Securities [Member]
Schedule Of Available For Sale Securities And Held To Maturity [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale		0
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale		0
Fair Value, 12 Months or Longer, Available-for-sale		0
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale		0
Fair Value, Available-for-sale		0
Gross Unrealized Holding Losses, Available-for-sale		$ 0
Fair Value, Less Than 12 Months, Held-to-maturity	0
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	0
Fair Value, 12 Months or Longer, Held-to-maturity	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0
Fair Value, Held-to-maturity	0
Gross Unrealized Holding Losses, Held-to-maturity	$ 0