Securities - Amortized Cost and Fair Value of Securities, by Contractual Maturities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule Of Securities [Line Items]
Available for Sale, Due in one year or less, Amortized Cost
Available for Sale, Due from one to five years, Amortized Cost	243,965
Available for Sale, Due from five to ten years, Amortized Cost	82,788
Available for Sale, Due after ten years, Amortized Cost	6,883
Available for Sale, with contractual maturities, Amortized Cost	333,636
Total securities available for sale, Amortized Cost	1,388,194	1,169,482
Available for Sale, Due in one year or less, Fair Value
Available for Sale, Due from one to five years, Fair Value	243,570
Available for Sale, Due from five to ten years, Fair Value	82,882
Available for Sale, Due after ten years, Fair Value	6,263
Available for Sale, with contractual maturities, Fair Value	332,715
Total available for sale Securities, Fair Value	1,384,273	1,141,650
Held to Maturity, Due in one year or less, Amortized Cost	3,435
Held to Maturity, Due from one to five years, Amortized Cost	90,689
Held to Maturity, Due from five to ten years, Amortized Cost	76,059
Held to Maturity, Due after ten years, Amortized Cost	75,776
Securities Held To Maturity, with contractual maturities, Amortized Cost	245,959
Held to Maturity, with contractual maturities, Amortized Cost	1,427,852	1,199,169
Held to Maturity, Due in one year or less, Fair Value	3,487
Held to Maturity, Due from one to five years, Fair Value	90,216
Held to Maturity, Due from five to ten years, Fair Value	77,683
Held to Maturity, Due after ten years, Fair Value	76,914
Securities Held To Maturity, with contractual maturities, Fair Value	248,300
Held to Maturity, with contractual maturities, Fair Value	1,439,241	1,189,563
Agency Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	427,873	247,880
Total available for sale Securities, Fair Value	435,075
Held to Maturity, with contractual maturities, Amortized Cost	715,611	628,681
Held to Maturity, with contractual maturities, Fair Value	732,222	634,930
Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	614,983	511,098
Total available for sale Securities, Fair Value	604,513
Held to Maturity, with contractual maturities, Amortized Cost	458,232	385,408
Held to Maturity, with contractual maturities, Fair Value	450,508	370,328
Non-Agency Collateralized Mortgage Obligations [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	1,612	1,747
Total available for sale Securities, Fair Value	1,625
Held to Maturity, with contractual maturities, Amortized Cost	5,823	6,852
Held to Maturity, with contractual maturities, Fair Value	5,837	6,892
Commercial Mortgage-Backed Securities [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	9,059
Total available for sale Securities, Fair Value	9,061
Held to Maturity, with contractual maturities, Amortized Cost	2,227	2,241
Held to Maturity, with contractual maturities, Fair Value	2,374	2,328
Equity Securities [Member]
Schedule Of Securities [Line Items]
Total securities available for sale, Amortized Cost	1,031	1,444
Total available for sale Securities, Fair Value	1,284
Held to Maturity, with contractual maturities, Amortized Cost
Held to Maturity, with contractual maturities, Fair Value