Amortized Costs and Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Equity securities, Amortized costs	$ 17,549	$ 17,441
Total, Amortized costs	548,727	528,833
Debt securities, Fair values	546,564
Equity securities, Fair values	22,479	20,695
Available for sale securities, Total	569,043	537,343
Municipal
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	51,429	47,808
Debt securities, Fair values	52,137	47,252
Corporate
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	291,951	285,104
Debt securities, Fair values	305,035	291,832
Foreign
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	173,468	164,146
Debt securities, Fair values	174,350	162,367
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	14,330	14,334
Debt securities, Fair values	$ 15,042	$ 15,197