Gross Unrealized Gains and Losses (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	$ 14,071	$ 23,030
Gross unrealized losses	5,166	854
Municipal
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	334	1,006
Gross unrealized losses	889	7
Corporate and utilities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	10,279	19,141
Gross unrealized losses	2,542	486
Foreign
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	388	1,210
Gross unrealized losses	1,577	286
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	1,034	1,395
Gross unrealized losses	46
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Gross unrealized gains	2,036	278
Gross unrealized losses	$ 112	$ 75