Reconciliation of all Assets Measured at Fair Value on Recurring Basis, Using Significant Unobservable Inputs (Level 3) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2012 Obligations of State and Political Subdivisions [Member]	Dec. 31, 2011 Obligations of State and Political Subdivisions [Member]	Dec. 31, 2012 Equity Securities [Member]	Dec. 31, 2011 Equity Securities [Member]	Dec. 31, 2012 Corporate Securities	Dec. 31, 2011 Corporate Securities
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance of Recurring Level 3 Assets at January 1		$ 4,075	$ 0	$ 353	$ 353	$ 1,005	$ 0
Total Gains or Losses (realized/unrealized)Included in earnings	0	156	0	0	0	0	0
Maturities / Calls	0	0	0	0	0	(1,005)	0
Purchases	0	7,938	4,075	0	0	0	1,005
Ending Balance of Recurring Level 3 Assets at December 31		$ 12,169	$ 4,075	$ 353	$ 353	$ 0	$ 1,005