Condensed Parent Company Financial Statements - Summary of Balance Sheet of Parent Company (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
ASSETS
Cash	$ 196,547	$ 213,103
Securities	527,627	562,542
Goodwill	44,545	44,545	44,545
Total assets	6,038,974	6,022,250	5,608,825
LIABILITIES AND STOCKHOLDERS' EQUITY
Other liabilities	24,126	21,300
Junior subordinated debentures	26,804	26,804
Stockholders' equity	556,997	519,567	483,041
Total liabilities and stockholders' equity	6,038,974	6,022,250
Parent Company [Member]
ASSETS
Cash	27,592	19,635
Securities	115	266
Investments in subsidiaries	555,761	523,312
Goodwill	450	450
Dividends receivable	5,927	1,465
Other assets	913	1,995
Total assets	590,758	547,123
LIABILITIES AND STOCKHOLDERS' EQUITY
Other liabilities	6,957	752
Junior subordinated debentures	26,804	26,804
Stockholders' equity	556,997	519,567
Total liabilities and stockholders' equity	$ 590,758	$ 547,123