Securities - Securities Available for Sale in Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less Than 12 Months	$ 439,024	$ 433,947
Unrealized Loss, Less Than 12 Months	(21,554)	(32,040)
Fair Value, 12 Months or More	76,657	75,365
Unrealized Loss, 12 Months or More	(6,664)	(8,728)
Total Fair Value	515,681	509,312
Total, Unrealized Loss	(28,218)	(40,768)
U.S. Treasury and Government Sponsored Entities' Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less Than 12 Months	200,991	193,746
Unrealized Loss, Less Than 12 Months	(13,899)	(21,360)
Fair Value, 12 Months or More	29,224	28,046
Unrealized Loss, 12 Months or More	(2,982)	(4,210)
Total Fair Value	230,215	221,792
Total, Unrealized Loss	(16,881)	(25,570)
Mortgage-Backed GSE Securities: Residential [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less Than 12 Months	238,033	240,201
Unrealized Loss, Less Than 12 Months	(7,655)	(10,680)
Fair Value, 12 Months or More	47,433	47,319
Unrealized Loss, 12 Months or More	(3,682)	(4,518)
Total Fair Value	285,466	287,520
Total, Unrealized Loss	$ (11,337)	$ (15,198)