Common Stock - Additional Information (Detail) (USD $)	12 Months Ended					12 Months Ended						12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2008	Dec. 30, 2012	Dec. 30, 2011	Dec. 31, 2012 Parent Company [Member]	Dec. 31, 2011 Parent Company [Member]	Dec. 31, 2010 Parent Company [Member]	Dec. 31, 2009 Parent Company [Member]	Dec. 31, 2008 Parent Company [Member] Warrant	Dec. 31, 2007 Parent Company [Member]	Dec. 31, 2012 Dividend Reinvestment Plan [Member]	Dec. 31, 2011 Dividend Reinvestment Plan [Member]	Dec. 31, 2010 Dividend Reinvestment Plan [Member]	Jun. 29, 2009 Dividend Reinvestment Plan [Member] Parent Company [Member]	Dec. 31, 2009 Warrants [Member]
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												721,000	705,000	681,000
Proceeds from treasury stock reissued												$ 8,000,000	$ 8,300,000	$ 8,400,000
Number of common stock issued upon exercise of warrant	489,000	489,000
Exercise price of warrant	11.30	11.30							15.64							16.12
Warrants issued										918,000
Amount of shares each warrant entitles buyer to			1.1025						1.2155
Number of shares repurchased						55,000	52,000	33,000								2,500,000
Number of shares authorized to repurchase											4,700,000
Preferred stock, shares issued	0	0		0	0
Average price of shares purchased						$ 9.41	$ 11.55	$ 11.88