Investment Securities - Summary of Continuous Unrealized Loss Position of Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	$ 434,489	$ 734,993
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	(5,906)	(8,671)
Fair Value, 12 Months or Longer, Available-for-sale	5,991	5,981
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	(1)	(1)
Fair Value, Available-for-sale	440,480	740,974
Gross Unrealized Holding Losses, Available-for-sale	(5,907)	(8,672)
Fair Value, Less Than 12 Months, Held-to-maturity	463,129	652,076
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(10,795)	(14,383)
Fair Value, 12 Months or Longer, Held-to-maturity	23,484	36,971
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	(907)	(1,057)
Fair Value, Held-to-maturity	486,613	689,047
Gross Unrealized Holding Losses, Held-to-maturity	(11,702)	(15,440)
CMO/REMIC - Residential [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	79,172	128,595
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	(951)	(1,485)
Fair Value, 12 Months or Longer, Available-for-sale	0	0
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	0	0
Fair Value, Available-for-sale	79,172	128,595
Gross Unrealized Holding Losses, Available-for-sale	(951)	(1,485)
Fair Value, Less Than 12 Months, Held-to-maturity	227,392	237,611
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(6,611)	(6,808)
Fair Value, 12 Months or Longer, Held-to-maturity	0	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0	0
Fair Value, Held-to-maturity	227,392	237,611
Gross Unrealized Holding Losses, Held-to-maturity	(6,611)	(6,808)
Government Agency/GSE [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	0	0
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	0	0
Fair Value, 12 Months or Longer, Available-for-sale	0	0
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	0	0
Fair Value, Available-for-sale	0	0
Gross Unrealized Holding Losses, Available-for-sale	0	0
Fair Value, Less Than 12 Months, Held-to-maturity	46,040	76,854
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(1,361)	(1,972)
Fair Value, 12 Months or Longer, Held-to-maturity	0	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0	0
Fair Value, Held-to-maturity	46,040	76,854
Gross Unrealized Holding Losses, Held-to-maturity	(1,361)	(1,972)
Residential Mortgage-backed Securities [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	339,074	583,143
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	(4,601)	(6,232)
Fair Value, 12 Months or Longer, Available-for-sale	0	0
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	0	0
Fair Value, Available-for-sale	339,074	583,143
Gross Unrealized Holding Losses, Available-for-sale	(4,601)	(6,232)
Fair Value, Less Than 12 Months, Held-to-maturity	111,873	191,807
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(393)	(1,892)
Fair Value, 12 Months or Longer, Held-to-maturity	0	0
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	0	0
Fair Value, Held-to-maturity	111,873	191,807
Gross Unrealized Holding Losses, Held-to-maturity	(393)	(1,892)
Municipal Bonds [Member]
Schedule of Investments [Line Items]
Fair Value, Less Than 12 Months, Available-for-sale	16,243	23,255
Gross Unrealized Holding Losses, Less Than 12 Months, Available-for-sale	(354)	(954)
Fair Value, 12 Months or Longer, Available-for-sale	5,991	5,981
Gross Unrealized Holding Losses, 12 Months or Longer, Available-for-sale	(1)	(1)
Fair Value, Available-for-sale	22,234	29,236
Gross Unrealized Holding Losses, Available-for-sale	(355)	(955)
Fair Value, Less Than 12 Months, Held-to-maturity	77,824	145,804
Gross Unrealized Holding Losses, Less Than 12 Months, Held-to-maturity	(2,430)	(3,711)
Fair Value, 12 Months or Longer, Held-to-maturity	23,484	36,971
Gross Unrealized Holding Losses, 12 Months or Longer, Held-to-maturity	(907)	(1,057)
Fair Value, Held-to-maturity	101,308	182,775
Gross Unrealized Holding Losses, Held-to-maturity	$ (3,337)	$ (4,768)