Share-Based Compensation - Additional Information (Detail) (USD $)			1 Months Ended	12 Months Ended			0 Months Ended	1 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2013 Stock and Incentive Compensation Plan	May 31, 2012 Directors Stock Compensation Plan	Dec. 31, 2013 Directors Stock Compensation Plan	Dec. 31, 2012 Directors Stock Compensation Plan	Dec. 31, 2011 Directors Stock Compensation Plan	Feb. 24, 2012 Performance Incentive Plan	Jul. 31, 2012 Performance Incentive Plan	Dec. 31, 2013 Performance Incentive Plan	Dec. 31, 2012 Performance Incentive Plan	Dec. 31, 2011 Performance Incentive Plan	Dec. 31, 2013 Additional Paid-In Capital	Dec. 31, 2012 Additional Paid-In Capital	Dec. 31, 2011 Additional Paid-In Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amortization of expense equally over a service period				1 year
Number of shares received by our non-employee directors			857
Weighted average grant-date fair value of awards granted				$ 52.49	$ 41.06	$ 41.02			$ 44.85	$ 39.62	$ 40.16
Unrecognized compensation expense related to the DSCP awards				$ 165,000
Shares reserved for issuance	580,484	441,241
Granted awards, shares					10,800			4,800	23,491	35,706
Number of shares withheld									10,411	5,670	12,234
Payments of employees' tax obligations to taxing authorities									519,000	238,000	496,000
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation												202,000	172,000	13,000
Intrinsic value of PIP awards									4,800,000	3,800,000	3,800,000
Cash payment received by executive officer							$ 181,500