Investment Securities (Investment Securities, Continuous Unrealized Loss Position, Fair Value) (Detail) $ in Thousands	Mar. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	$ 141,264
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(425)
Continuous unrealized losses existing for greater than 12 months, Fair value	181,950
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(4,145)
Total, Fair value	323,214
Total, Unrealized losses	(4,570)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	224,324
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(1,580)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,917
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(32)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	229,241
Held-to-maturity Securities, Continuous Unrealized Loss Position, Unrealized Losses	(1,612)
U.S. Treasury
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	75,049
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(38)
Continuous unrealized losses existing for greater than 12 months, Fair value	0
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	0
Total, Fair value	75,049
Total, Unrealized losses	(38)
U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	13,982
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(10)
Continuous unrealized losses existing for greater than 12 months, Fair value	1,833
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(2)
Total, Fair value	15,815
Total, Unrealized losses	(12)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	208,405
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(1,455)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	0
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	208,405
Held-to-maturity Securities, Continuous Unrealized Loss Position, Unrealized Losses	(1,455)
Municipal
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	18,399
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(40)
Continuous unrealized losses existing for greater than 12 months, Fair value	6,977
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(184)
Total, Fair value	25,376
Total, Unrealized losses	(224)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	15,919
Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Unrealized Losses	(125)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	4,917
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Unrealized Losses	(32)
Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value	20,836
Held-to-maturity Securities, Continuous Unrealized Loss Position, Unrealized Losses	(157)
Corporate notes, Financial issuers
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	22,952
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(237)
Continuous unrealized losses existing for greater than 12 months, Fair value	34,367
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(1,593)
Total, Fair value	57,319
Total, Unrealized losses	(1,830)
Corporate notes, Other
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	0
Continuous unrealized losses existing for less than 12 months, Unrealized losses	0
Continuous unrealized losses existing for greater than 12 months, Fair value	0
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	0
Total, Fair value	0
Total, Unrealized losses	0
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	2,038
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(3)
Continuous unrealized losses existing for greater than 12 months, Fair value	122,371
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(1,897)
Total, Fair value	124,409
Total, Unrealized losses	(1,900)
Mortgage-backed, Collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	4,880
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(42)
Continuous unrealized losses existing for greater than 12 months, Fair value	7,803
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(156)
Total, Fair value	12,683
Total, Unrealized losses	(198)
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Continuous unrealized losses existing for less than 12 months, Fair value	3,964
Continuous unrealized losses existing for less than 12 months, Unrealized losses	(55)
Continuous unrealized losses existing for greater than 12 months, Fair value	8,599
Continuous unrealized losses existing for greater than 12 months, Unrealized losses	(313)
Total, Fair value	12,563
Total, Unrealized losses	$ (368)