Amortized Costs and Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Equity securities, Amortized costs	$ 17,441	$ 17,441
Total, Amortized costs	543,856	528,833
Debt securities, Fair values	537,267
Equity securities, Fair values	21,300	20,695
Available for sale securities, Total	558,567	537,343
Municipal
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	58,110	47,808
Debt securities, Fair values	58,111	47,252
Corporate
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	292,770	285,104
Debt securities, Fair values	302,852	291,832
Foreign
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	161,203	164,146
Debt securities, Fair values	161,192	162,367
U.S. Government
Schedule of Available-for-sale Securities [Line Items]
Debt securities, Amortized costs	14,332	14,334
Debt securities, Fair values	$ 15,112	$ 15,197