Share-Based Compensation Plans - Summary of Stock Activity under DSCP (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended
	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	Jul. 31, 2012 Performance Incentive Plan	Dec. 31, 2013 Performance Incentive Plan	Dec. 31, 2012 Performance Incentive Plan		Dec. 31, 2011 Performance Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares, Outstanding Beginning Balance		0	0			84,645	87,414
Number of Shares, Granted			10,800		4,800	23,491	35,706
Number of Shares, Vested		9,427	10,800			24,332	13,837
Number of Shares, Forfeited							21,600	[1]
Number of Shares, Outstanding Ending Balance		0	0	0		80,761	84,645		87,414
Number of shares withheld						10,411	5,670		12,234
Payments of employees' tax obligations to taxing authorities						$ 519	$ 238		$ 496
Number of shares received by our non-employee directors	857
Weighted Average Grant Date Fair Value, Outstanding Beginning Balance		$ 0.00	$ 0.00			$ 37.86	$ 34.47
Weighted Average Grant Date Fair Value, Granted		$ 52.49	$ 41.06	$ 41.02		$ 44.85	$ 39.62		$ 40.16
Weighted Average Grant Date Fair Value, Vested			$ 41.06			$ 33.26	$ 29.19
Weighted Average Grant Date Fair Value, Forfeited							$ 36.57	[1]
Weighted Average Grant Date Fair Value, Outstanding Ending Balance		$ 0.00	$ 0.00	$ 0.00		$ 42.30	$ 37.86		$ 34.47
Unrecognized compensation expense related to the DSCP awards		$ 165

[1] Includes shares settled with a cash payment pursuant to the terms of a separation agreement with a former named executive officer.