Gross Unrealized Losses on Investments and Fair Values of Related Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	$ 4,062	$ 736
Fair Values, Less than 12 months	162,540	74,488
Losses, More than 12 months	2,192	118
Fair Values, More than 12 months	76,145	59,538
Total Losses	6,254	854
Total Fair Values	238,685	134,026
Municipal
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	770	7
Fair Values, Less than 12 months	27,686	697
Losses, More than 12 months	43
Fair Values, More than 12 months	628
Total Losses	813	7
Total Fair Values	28,314	697
Corporate
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	1,682	486
Fair Values, Less than 12 months	66,776	30,538
Losses, More than 12 months	1,546
Fair Values, More than 12 months	21,710
Total Losses	3,228	486
Total Fair Values	88,486	30,538
Foreign
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	1,539	168
Fair Values, Less than 12 months	63,039	41,056
Losses, More than 12 months	603	118
Fair Values, More than 12 months	53,807	59,538
Total Losses	2,142	286
Total Fair Values	116,846	100,594
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	60
Fair Values, Less than 12 months	3,772
Total Losses	60
Total Fair Values	3,772
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	11	75
Fair Values, Less than 12 months	1,267	2,197
Total Losses	11	75
Total Fair Values	$ 1,267	$ 2,197