Gross Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	$ 12,883	$ 23,030
Gross unrealized losses	5,439	854
Municipal
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	250	1,006
Gross unrealized losses	899	7
Corporate and utilities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	9,527	19,141
Gross unrealized losses	2,927	486
Foreign
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	298	1,210
Gross unrealized losses	1,548	286
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,098	1,395
Gross unrealized losses	65
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,710	278
Gross unrealized losses		$ 75