Amortized Costs and Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Equity securities, Amortized costs	$ 17,441	$ 10,870
Total, Amortized costs	528,833	481,083
Debt securities, Fair values	516,648
Equity securities, Fair values	20,695	11,073
Available for sale securities, Total	537,343	503,259
Municipal
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	47,808	18,012
Debt securities, Fair values	47,252	19,011
Corporate
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	285,104	268,874
Debt securities, Fair values	291,832	287,528
Foreign
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	164,146	168,084
Debt securities, Fair values	162,367	169,009
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	14,334	15,243
Debt securities, Fair values	$ 15,197	$ 16,638