Amortized Cost and Estimated Fair Values of Investments Held-To-Maturity (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 223,747	$ 224,638
Gross Unrealized Gains	2,813	1,949
Gross Unrealized Losses	(5,867)	(10,580)
Estimated Fair Value	220,693	216,007
U.S. Government Agencies
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	64,507	64,505
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(3,010)	(4,827)
Estimated Fair Value	61,497	59,678
State and municipal
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	159,012	159,889
Gross Unrealized Gains	2,786	1,920
Gross Unrealized Losses	(2,857)	(5,753)
Estimated Fair Value	158,941	156,056
Mortgage-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	228	244
Gross Unrealized Gains	27	29
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 255	$ 273