Stock Option Plan and Stock Grants - Additional Information (Detail) (USD $)	1 Months Ended						12 Months Ended			1 Months Ended					3 Months Ended	12 Months Ended			25 Months Ended	1 Months Ended											3 Months Ended	12 Months Ended				1 Months Ended
	Apr. 30, 2013	Feb. 28, 2013	May 08, 2012	May 11, 2011	Jan. 31, 2011	Feb. 28, 2010	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	May 31, 2013 Director [Member]	Mar. 31, 2013 Director [Member]	Jan. 31, 2013 Director [Member]	Jan. 31, 2012 Director [Member]	Jan. 31, 2012 Senior Management	Mar. 31, 2011 Restricted Stock [Member]	Dec. 31, 2013 Restricted Stock [Member]	Dec. 31, 2012 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	May 31, 2013 Restricted Stock [Member]	May 31, 2013 Restricted Stock [Member] Director [Member]	Mar. 31, 2013 Restricted Stock [Member] Director [Member]	Jan. 31, 2013 Restricted Stock [Member] Director [Member]	May 08, 2012 Restricted Stock [Member] Director [Member]	Jan. 31, 2012 Restricted Stock [Member] Director [Member]	May 11, 2011 Restricted Stock [Member] Director [Member]	Jan. 31, 2011 Restricted Stock [Member] Director [Member]	Apr. 30, 2013 Restricted Stock [Member] Senior Management	Feb. 28, 2013 Restricted Stock [Member] Senior Management	Jan. 31, 2012 Restricted Stock [Member] Senior Management	Feb. 28, 2011 Restricted Stock [Member] Senior Management	Sep. 30, 2012 Restricted Stock [Member] Senior Management	Dec. 31, 2013 Restricted Stock [Member]	Dec. 31, 2012 Restricted Stock [Member]	Dec. 31, 2011 Restricted Stock [Member]	Dec. 31, 2010 Restricted Stock [Member]	May 31, 2013 Phase One [Member] Restricted Stock [Member] Director [Member]	Mar. 31, 2013 Phase One [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2013 Phase One [Member] Restricted Stock [Member] Director [Member]	May 08, 2012 Phase One [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2012 Phase One [Member] Restricted Stock [Member] Director [Member]	May 11, 2011 Phase One [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2011 Phase One [Member] Restricted Stock [Member] Director [Member]	May 31, 2013 Phase Two [Member] Restricted Stock [Member] Director [Member]	Mar. 31, 2013 Phase Two [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2013 Phase Two [Member] Restricted Stock [Member] Director [Member]	May 08, 2012 Phase Two [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2012 Phase Two [Member] Restricted Stock [Member] Director [Member]	May 11, 2011 Phase Two [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2011 Phase Two [Member] Restricted Stock [Member] Director [Member]	May 31, 2013 Phase Three [Member] Restricted Stock [Member] Director [Member]	Mar. 31, 2013 Phase Three [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2013 Phase Three [Member] Restricted Stock [Member] Director [Member]	May 08, 2012 Phase Three [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2012 Phase Three [Member] Restricted Stock [Member] Director [Member]	May 11, 2011 Phase Three [Member] Restricted Stock [Member] Director [Member]	Jan. 31, 2011 Phase Three [Member] Restricted Stock [Member] Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodNetOfForfeitures																																99,788	94,020	94,020	104,686
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period																																(167,564)	(177,998)	(227,330)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value																																$ 34.97	$ 32.30	$ 24.50
Stock Issued During Period, Shares, Restricted Stock Award, Gross							173,332	214,664	239,330
Stock Issued During Period, Shares, Restricted Stock Award, Forfeited								(36,666)	(22,666)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value																																	$ 35.07	$ 28.70
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value							$ 500,000	$ 1,700,000	$ 6,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value							15,500,000	13,100,000	14,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period															207,330				383,330	40,000	666	62,000	32,000	62,000	32,000	62,000	2,000	68,666	120,664	145,330
Share based compensation, fair market value																				1,700,000	0	2,200,000	1,100,000	2,200,000	900,000	1,800,000	80,200	2,500,000	4,200,000	4,200,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights	These Restricted Stock Grants will vest on December 31, 2013.	These Restricted Stock Grants will vest on December 31, 2013.	One-third of the shares of restricted common stock covered by these awards vests on each of November 8, 2012, May 8, 2013, and May 8, 2014.	One-third of the shares of restricted common stock covered by these awards vests on each of November 11, 2011, May 11, 2012, and May 11, 2013.	One-third of the shares of restricted common stock covered by these awards vests on each of December 31, 2011, December 31, 2012, and December 31, 2013.	These Restricted Stock Grants vested December 31, 2011.				One-third of the shares of restricted common stock covered by these awards vest on each of November 8, 2013, May 8, 2014, and May 8, 2015.	One-third of the shares of restricted common stock covered by these awards vests on each of September 13, 2013, March 13, 2014, and March 13, 2015.	of the shares of restricted common stock covered by these awards vest on each of December 31, 2013, December 31, 2014, and December 31, 2015.	One-third of the shares of restricted common stock covered by these awards vests on each of December 31, 2012, December 31, 2013, and December 31, 2014.	These Restricted Stock Grants vested on December 31, 2012.
Share based compensation, restricted stock, vesting date																											Dec. 31, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011						Nov. 08, 2013	Sep. 13, 2013	Dec. 31, 2013	Nov. 08, 2012	Dec. 31, 2012	Nov. 11, 2011	Dec. 31, 2011	May 08, 2014	Mar. 13, 2014	Dec. 31, 2014	May 08, 2013	Dec. 31, 2013	May 11, 2012	Dec. 31, 2012	May 08, 2015	Mar. 13, 2015	Dec. 31, 2015	May 08, 2014	Dec. 31, 2014	May 11, 2013	Dec. 31, 2013
Share based compensation expense, restricted stock grant																6,000,000	5,800,000	5,800,000
Share based compensation expense to be recognized																3,300,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition																1 year 4 months 25 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period									344,768																						36,666
DeferredCompensationArrangementWithIndividualFairValueOfSharesCancelled																															$ 1,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value																																$ 37.32	$ 35.06	$ 28.75
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value																																$ 37.17	$ 32.97	$ 27.75	$ 18.61