Stock Option Plans, Stock Grants, Stock Appreciation Rights and Employee Stock Purchase Plan - Additional Information (Detail) (USD $)	12 Months Ended					12 Months Ended		12 Months Ended					12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Maximum	May 31, 2005 2005 Stock Incentive Plan	Dec. 31, 2011 Amended And Restated 2005 Stock Incentive Plan	Apr. 30, 2009 Amended And Restated 2005 Stock Incentive Plan	Dec. 31, 2011 Options and Non Performance Based Grants	Dec. 31, 2011 Non Performance Based Shares	Dec. 31, 2011 Performance Based Shares Issued in 2011	Dec. 31, 2011 Performance Based Shares Issued in 2011 Maximum	Dec. 31, 2011 Performance Based Shares Issued in 2011 Minimum	Dec. 31, 2011 Performance Based Shares Issued Prior to 2011	Dec. 31, 2011 Performance Based Shares Issued Prior to 2011 Maximum	Dec. 31, 2011 Performance Based Shares Issued Prior to 2011 Minimum	Dec. 31, 2011 Stock appreciation rights Maximum	Dec. 31, 2011 Stock appreciation rights Minimum	Dec. 31, 2011 Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock authorized for issuance					1,000,000		1,500,000									300,000
Stock issued during period under incentive plan						1,073,825
Number of stock available to be issued						426,175
Share based payment award, award vesting period								4 years	5 years	3 years			5 years
Vesting Percentage of share in year three									33.33%				33.33%
Percentage of shares vesting over the period										50.00%
Vesting Percentage of share in year four									33.33%				33.33%
Percentage of remaining shares vesting over the period dependent on compound annual growth book value per share immediately prior to vesting date										50.00%
Vesting Percentage of share in year five									33.33%				33.33%
Options expiration term (in years)				10 years
Percentage of shares vesting range											150.00%	0.00%		150.00%	0.00%
Exercise price as percentage of fair market value																	90.00%	90.00%
Percentage of employees base compensation through payroll that can be invested for the purchase of common stock, maximum	10.00%
Number of shares which can be acquired by employee, maximum	1,000
Total market value of shares that can be acquired by employee	$ 25,000
Employee Stock Purchase Plan, shares to be purchased in following period	7,346
Employee Stock Purchase Plan, shares purchased by employees	19,074	22,000	17,000