Common Stock - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended	12 Months Ended					12 Months Ended				12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jul. 31, 2008 Parent Company [Member] Warrant	Dec. 31, 2013 Parent Company [Member]	Dec. 31, 2012 Parent Company [Member]	Dec. 31, 2011 Parent Company [Member]	Dec. 31, 2010 Parent Company [Member]	Dec. 31, 2007 Parent Company [Member]	Dec. 31, 2013 Dividend Reinvestment Plan [Member]	Dec. 31, 2012 Dividend Reinvestment Plan [Member]	Dec. 31, 2011 Dividend Reinvestment Plan [Member]	Jun. 29, 2009 Dividend Reinvestment Plan [Member] Parent Company [Member]	Dec. 31, 2009 Warrants [Member] Parent Company [Member]
Common Stock [Line Items]
Common stock, shares authorized	232,023,233	232,023,233											10,000,000
Maximum voluntary optional cash payments made by shareholders to purchase common shares	$ 100,000
Number of shares reissued from treasury stock										775,000	721,000	705,000
Proceeds from treasury stock reissued										$ 7,600,000	$ 8,000,000	$ 8,300,000
Number of common stock issued upon exercise of warrant	489,000	489,000	489,000
Exercise price of warrant	11.30	11.30	11.30	15.64				16.12
Warrant exercise period	10 years	10 years
Warrants issued				918,000
Amount of shares each warrant entitles buyer to purchase				1.2155				1.1030
Expiration date of issued warrants				Jun. 30, 2015				Nov. 14, 2018
Number of shares repurchased					78,000	55,000	52,000							2,500,000
Number of shares authorized to repurchase									4,700,000
Number of shares repurchased during the period					0
Average price of shares purchased					$ 9.91	$ 9.41	$ 11.55