Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investments Debt And Equity Securities [Abstract]
Securities Available for Sale, Weighted Average Yield, Within one year or less	2.10%
Securities Available for Sale, Weighted Average Yield, One through five years	1.45%
Securities Available for Sale, Weighted Average Yield, After five through ten years	2.12%
Securities Available for Sale, Weighted Average Yield, Over ten years	2.23%
Securities Available for Sale, Weighted Average Yield, Totals	2.11%
Securities Available for Sale, Amortized Cost, Within one year or less	$ 17,460
Securities Available for Sale, Amortized Cost, One through five years	228,767
Securities Available for Sale, Amortized Cost, After five through ten years	514,550
Securities Available for Sale, Amortized Cost, Over ten years	1,182,918
Securities Available for Sale, Amortized Cost, Totals	1,943,695
Securities Available for Sale, Estimated Fair Value, Within one year or less	17,563
Securities Available for Sale, Estimated Fair Value, One through five years	227,952
Securities Available for Sale, Estimated Fair Value, After five through ten years	512,892
Securities Available for Sale, Estimated Fair Value, Over ten years	1,174,907
Securities Available for Sale, Estimated Fair Value, Totals	1,933,314
Securities Held to Maturity, Weighted Average Yield, Within one year or less	1.84%
Securities Held to Maturity, Weighted Average Yield, One through five years	2.86%
Securities Held to Maturity, Weighted Average Yield, After five through ten years	2.78%
Securities Held to Maturity, Weighted Average Yield, Over ten years	3.08%
Securities Held to Maturity, Weighted Average Yield, Totals	2.80%
Securities Held to Maturity, Amortized Cost, Within one year or less	24,484
Securities Held to Maturity, Amortized Cost, One through five years	22,641
Securities Held to Maturity, Amortized Cost, After five through ten years	19,928
Securities Held to Maturity, Amortized Cost, Over ten years	83,607
Securities Held to Maturity, Amortized Cost, Totals	150,660	154,109
Securities Held to Maturity, Estimated Fair Value, Within one year or less	24,558
Securities Held to Maturity, Estimated Fair Value, One through five years	23,260
Securities Held to Maturity, Estimated Fair Value, After five through ten years	20,272
Securities Held to Maturity, Estimated Fair Value, Over ten years	82,873
Securities Held to Maturity, Estimated Fair Value, Totals	$ 150,963	$ 152,566