Income Taxes - Summary of Differences in Taxes Computed at Statutory Rate (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Tax Disclosure [Abstract]
Provision at statutory rate of 35%	$ 9,251	$ 14,774	$ 21,764	$ 26,792
Tax-exempt income	(3,422)	(3,092)	(6,559)	(5,989)
State income taxes	182	1,156	825	2,372
State statutory rate change	(218)	1,257	904	1,257
Interim period effective rate adjustment	2,149	(358)	124	(223)
Other, net	(284)	(3)	(158)	(83)
Income tax expense	$ 7,658	$ 13,734	$ 16,900	$ 24,126
Effective tax rate	29.00%	32.50%	27.20%	31.50%