Fair Value (Carrying Amounts and Fair Values of Company's Financial Instruments) (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Financial Assets
Investments held-to-maturity and other equity securities	$ 258,762	$ 265,325
Loans, net of allowance	2,938,338	2,784,266
Other assets	88,031	86,213
Financial Liabilities
Time deposits	450,654	465,737
Securities sold under retail repurchase agreements and federal funds purchased	71,384	53,842
Advances from FHLB	558,000	615,000
Subordinated debentures	35,000	35,000
Financial Assets
Investments held-to-maturity and other equity securities	223,130	216,007
Fair Value, Measurements, Recurring
Financial Assets
Investments held-to-maturity and other equity securities	260,202	256,694
Loans, net of allowance	2,882,093	2,692,877
Other assets	88,031	86,213
Financial Liabilities
Time deposits	450,323	465,392
Securities sold under retail repurchase agreements and federal funds purchased	71,384	53,842
Advances from FHLB	580,738	641,901
Subordinated debentures	12,652	11,376
Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring
Financial Assets
Investments held-to-maturity and other equity securities	260,202	256,694
Other assets	88,031	86,213
Financial Liabilities
Time deposits	450,323	465,392
Securities sold under retail repurchase agreements and federal funds purchased	71,384	53,842
Advances from FHLB	580,738	641,901
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring
Financial Assets
Loans, net of allowance	2,882,093	2,692,877
Financial Liabilities
Subordinated debentures	$ 12,652	$ 11,376