Gross Unrealized Losses on Investments and Fair Values of Related Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	$ 830	$ 4,062
Fair Values, Less than 12 months	60,967	162,540
Losses, More than 12 months	1,191	2,192
Fair Values, More than 12 months	62,280	76,145
Total Losses	2,021	6,254
Total Fair Values	123,247	238,685
Municipal
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	2	770
Fair Values, Less than 12 months	719	27,686
Losses, More than 12 months	218	43
Fair Values, More than 12 months	18,888	628
Total Losses	220	813
Total Fair Values	19,607	28,314
Corporate
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	29	1,682
Fair Values, Less than 12 months	998	66,776
Losses, More than 12 months	826	1,546
Fair Values, More than 12 months	33,157	21,710
Total Losses	855	3,228
Total Fair Values	34,155	88,486
Foreign
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	571	1,539
Fair Values, Less than 12 months	58,245	63,039
Losses, More than 12 months	116	603
Fair Values, More than 12 months	6,673	53,807
Total Losses	687	2,142
Total Fair Values	64,918	116,846
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	0	60
Fair Values, Less than 12 months	125	3,772
Losses, More than 12 months	31	0
Fair Values, More than 12 months	3,562	0
Total Losses	31	60
Total Fair Values	3,687	3,772
Equity securities
Schedule of Available-for-sale Securities [Line Items]
Losses, Less than 12 months	228	11
Fair Values, Less than 12 months	880	1,267
Losses, More than 12 months	0	0
Fair Values, More than 12 months	0	0
Total Losses	228	11
Total Fair Values	$ 880	$ 1,267