Condensed Parent Company Financial Statements- Summary of Income Statement of Parent Company (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
OPERATING INCOME
Interest on interest-bearing deposits									$ 4,064	$ 4,201	$ 3,537
Other									6,250	7,504	7,430
OPERATING EXPENSE
Other									32,823	32,832	30,479
Income before taxes									80,842	79,004	70,697
Allocated income tax benefit									(26,525)	(27,104)	(25,076)
Amortization of stock-based compensation arrangements of subsidiaries									(1,360)	(1,530)	(3,075)
Net income	13,861	14,491	12,593	13,372	12,306	13,860	11,729	14,005	54,317	51,900	45,621
Parent Company [Member]
OPERATING INCOME
Dividends from subsidiaries									22,612	20,784	19,011
Interest on interest-bearing deposits									47	57	20
Other									92		88
Total operating income									22,751	20,841	19,119
OPERATING EXPENSE
Interest									1,965	2,134	2,501
Other									661	942	740
Total operating expense									2,626	3,076	3,241
Income before taxes									20,125	17,765	15,878
Allocated income tax benefit									978	1,371	886
Income before equity in undistributed earnings of subsidiaries									21,103	19,136	16,764
Equity in undistributed earnings of subsidiaries									34,351	34,281	31,856
Amortization of stock-based compensation arrangements of subsidiaries									(1,137)	(1,517)	(2,999)
Net income									$ 54,317	$ 51,900	$ 45,621