Gross Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	$ 23,030	$ 14,463
Gross unrealized losses	854	3,030
Municipal
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,006	1,080
Gross unrealized losses	7
Corporate and utilities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	19,141	9,184
Gross unrealized losses	486	2,973
Foreign
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,210	1,937
Gross unrealized losses	286	53
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,395	1,820
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	278	442
Gross unrealized losses	$ 75	$ 4