Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended				12 Months Ended
	Nov. 30, 2011	Apr. 30, 2008	Dec. 31, 2012 Vote	Sep. 30, 2012	Jul. 01, 2012	Apr. 01, 2012	Dec. 31, 2012 Vote	Dec. 31, 2011	Dec. 31, 2010	Dec. 05, 2008 Right
Equity [Line Items]
Authorized shares			400,000				400,000
Preferred stock issued			0				0
Preferred stock Par value			$ 0.01				$ 0.01
Vote entitled for each common share outstanding			1				1
Number of preferred stock purchase right for dividend distribution										1
Outstanding common share to be acquiring person			15.00%				15.00%
Repurchase of authorized common stock	$ 80,000,000	$ 50,000,000
Repurchase of shares			1,375,875				1,375,875
Repurchase of shares, Value			30,000,000				30,000,000
Remaining repurchase authorization amount	20,000,000
Cash dividend declared per common share			$ 0.11	$ 0.11	$ 0.11	$ 0.10
Additional dividend declared and paid			$ 0.11
Special dividend declared and paid			$ 1.00
Payment of dividends							$ 66,213,000	$ 15,114,000	$ 10,014,000