Income Taxes - Income Tax Expense from Operations from the Amount Computed by Applying the U.S. Federal Income Tax Statutory Rate of 35% to Income Before Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Expense Benefit From Continuing Operations [Line Items]
Income tax computed at federal statutory tax rate	$ 20,721	$ 13,000
Tax-exempt interest, net	(5,458)	(5,333)
State income tax	504	302
Dividends received deduction	(113)	(79)
Valuation allowance
Other	(87)	(100)
Income tax expense, Total	15,567	7,790	3,176
As Adjusted [Member]
Income Tax Expense Benefit From Continuing Operations [Line Items]
Income tax computed at federal statutory tax rate			9,575
Tax-exempt interest, net			(5,105)
State income tax			172
Dividends received deduction			(29)
Valuation allowance			(1,442)
Other			5
Income tax expense, Total			$ 3,176