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
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Performance Based Shares	Dec. 31, 2012 Performance Based Shares	Dec. 31, 2011 Performance Based Shares	Dec. 31, 2013 Maximum	Dec. 31, 2005 2005 Stock Incentive Plan	Dec. 31, 2013 Amended And Restated 2005 Stock Incentive Plan	Apr. 30, 2013 Amended And Restated 2005 Stock Incentive Plan	Apr. 30, 2009 Amended And Restated 2005 Stock Incentive Plan	Dec. 31, 2013 Options and Non Performance Based Grants Minimum	Dec. 31, 2013 Options and Non Performance Based Grants Maximum	Dec. 31, 2013 Non Performance Based Shares	Dec. 31, 2013 Non Performance Based Shares Year Three	Dec. 31, 2013 Non Performance Based Shares Year Four	Dec. 31, 2013 Non Performance Based Shares Year Five	Dec. 31, 2013 Performance Based Shares Issued in 2011	Dec. 31, 2013 Restricted stock units Minimum	Dec. 31, 2013 Restricted stock units Maximum	Dec. 31, 2013 Performance Based Shares Issued Prior to 2011	Dec. 31, 2013 Performance Based Shares Issued Prior to 2011 Year Three	Dec. 31, 2013 Performance Based Shares Issued Prior to 2011 Year Four	Dec. 31, 2013 Performance Based Shares Issued Prior to 2011 Year Five	Dec. 31, 2013 Performance Based Shares Issued Prior to 2011 Minimum	Dec. 31, 2013 Performance Based Shares Issued Prior to 2011 Maximum	Dec. 31, 2013 Stock appreciation rights	Dec. 31, 2012 Stock appreciation rights	Dec. 31, 2011 Stock appreciation rights	Dec. 31, 2013 Stock appreciation rights Minimum	Dec. 31, 2013 Restricted stock units	Dec. 31, 2012 Restricted stock units	Dec. 31, 2011 Restricted stock units	Dec. 31, 2013 Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock authorized for issuance								1,000,000		2,000,000	1,500,000																300,000
Stock issued during period under incentive plan									1,340,885
Number of stock available to be issued									659,115
Share based payment award, award vesting period												3 years	4 years	5 years				3 years			5 years
Options expiration term (in years)							10 years
Percentage of shares vesting over the period															33.33%	33.33%	33.33%	50.00%	0.00%	150.00%		33.33%	33.33%	33.33%	0.00%	150.00%
Percentage of remaining shares vesting over the period dependent on compound annual growth book value per share immediately prior to vesting date																		50.00%
Performance based shares that vested	133,482	138,321	215,065	15,714	0	22,933
Fair value of total vested shares	$ 3,500,000	$ 4,600,000	$ 8,600,000
Weighted average grant date fair value of all RSU granted																															$ 55.36	$ 48.21	$ 50.06
Unrecognized compensation expense, net of estimated forfeitures																															10,600,000	11,900,000
Weighted Average Periods																															2 years 2 months 12 days	2 years 2 months 12 days
Aggregate fair value of all unvested RSU																															39,600,000	30,000,000
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	8,738
Employee Stock Purchase Plan, shares purchased by employees	17,640	16,000	19,000
Discount on employee stock purchase plan	10.00%