Long -Term Borrowings - Debentures and Related Weighted Average Interest Rates (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Amount	$ 198,628	$ 198,515
Century Trust [Member]
Debt Instrument [Line Items]
Amount	8,800	8,800
Weighted-Average Rate	10.88%	10.88%
Sequoia Trust I [Member]
Debt Instrument [Line Items]
Amount	2,065	2,064
Weighted-Average Rate	10.18%	10.18%
United Statutory Trust III [Member]
Debt Instrument [Line Items]
Amount	20,619	20,619
Weighted-Average Rate	3.10%	3.16%
United Statutory Trust IV [Member]
Debt Instrument [Line Items]
Amount	25,774	25,774
Weighted-Average Rate	3.09%	3.16%
United Statutory Trust V [Member]
Debt Instrument [Line Items]
Amount	51,547	51,547
Weighted-Average Rate	1.80%	1.91%
United Statutory Trust VI [Member]
Debt Instrument [Line Items]
Amount	30,928	30,928
Weighted-Average Rate	1.54%	1.61%
Premier Statutory Trust II [Member]
Debt Instrument [Line Items]
Amount	6,186	6,186
Weighted-Average Rate	3.34%	3.44%
Premier Statutory Trust III [Member]
Debt Instrument [Line Items]
Amount	8,248	8,248
Weighted-Average Rate	1.98%	2.05%
Premier Statutory Trust IV [Member]
Debt Instrument [Line Items]
Amount	14,433	14,433
Weighted-Average Rate	1.80%	1.86%
Premier Statutory Trust V [Member]
Debt Instrument [Line Items]
Amount	10,310	10,310
Weighted-Average Rate	1.85%	1.92%
Centra Statutory Trust I [Member]
Debt Instrument [Line Items]
Amount	9,859	9,803
Weighted-Average Rate	2.54%	2.60%
Centra Statutory Trust II [Member]
Debt Instrument [Line Items]
Amount	$ 9,859	$ 9,803
Weighted-Average Rate	1.89%	1.99%