Income Taxes - Schedule of Income Taxes Reconciliation with Federal Statutory Rates (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
Income Tax Disclosure [Abstract]
Federal tax expense at statutory rates									$ 7,406	$ 7,481	$ 5,019
Tax credits									(28,421)	(17,100)	(13,142)
Tax credit-basis reduction									2,019	2,767	3,112
Tax-exempt income									(832)	(655)	(509)
Change in deferred rate											293
Disallowed interest expense									117	99	101
Other									(40)	(157)	(281)
Income tax benefit	$ (5,867)	$ (5,673)	$ (4,198)	$ (4,013)	$ 443	$ (3,130)	$ (2,952)	$ (1,926)	$ (19,751)	$ (7,565)	$ (5,407)