Stockholders' Equity - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			0 Months Ended	9 Months Ended		3 Months Ended	9 Months Ended		9 Months Ended	0 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Oct. 16, 2014 Subsequent Event [Member]	Sep. 30, 2014 Common Stock [Member]	Sep. 30, 2013 Common Stock [Member]	Sep. 30, 2014 Share Repurchase Plan [Member]	Sep. 30, 2014 Share Repurchase Plan [Member]	Mar. 18, 2014 Share Repurchase Plan [Member]	Sep. 30, 2014 Share Repurchase Plan [Member] Common Stock [Member]	Jun. 02, 2014 Series A Preferred Stock [Member]	Feb. 04, 2014 Series A Preferred Stock [Member]	Sep. 30, 2014 Series A Preferred Stock [Member]	Sep. 30, 2013 Series A Preferred Stock [Member]	Jun. 02, 2014 Series A Preferred Stock [Member]
Subsequent Event [Line Items]
Common stock repurchase authorized amount											$ 40,000,000
Time through the company is allowed to repurchase shares										Mar. 31, 2015
Common stock repurchased and retired, shares							14,070	26,705	246,578	734,924		734,924
Common stock repurchased and retired, weighted average price									$ 40.56	$ 37.83
Stock repurchased and retired, total costs			616,000	893,000					10,005,000	27,815,000
Fees and commissions average price repurchase common stock									$ 40.58	$ 37.85
Stock repurchase program available repurchase amount									$ 12,200,000	$ 12,200,000
Dividends per common share declared	$ 0.28	$ 0.22	$ 0.83	$ 0.68		$ 0.275
Date of dividend payable						Dec. 19, 2014
Record date of dividend payable						Nov. 21, 2014
Preferred stock conversion cancellation date															Apr. 01, 2014
Preferred stock Dividends rate														7.00%
Shares of Series A Preferred redeemed													3,386		(3,386)
Shares of Series A Preferred redeemed, per share																	$ 10
Conversion of preferred stock to common stock, shares							107,298	91,263							(107,298)	(91,263)
Preferred stock, outstanding	0		0		0										0