Summary of Restricted Stock Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Weighted Average Grant Date Fair Value
Schedule of Share based Compensation Arrangements by Share based Payment Award, Equity Instruments, Other Than Options, Restricted Stock Units [Line Items]
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 40.17	$ 40.93	$ 41.12
Granted, Weighted Average Grant Date Fair Value	$ 37.01	$ 42.08	$ 42.77
Vested, Weighted Average Grant Date Fair Value	$ 36.19	$ 44.40	$ 47.92
Forfeited, Weighted Average Grant Date Fair Value	$ 40.47	$ 41.23	$ 40.73
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 40.15	$ 40.17	$ 40.93
Performance-Based Weighted Average Grant Date Fair Value
Schedule of Share based Compensation Arrangements by Share based Payment Award, Equity Instruments, Other Than Options, Restricted Stock Units [Line Items]
Outstanding, beginning of period, Weighted Average Grant Date Fair Value	$ 45.37	$ 39.62	$ 42.79
Granted, Weighted Average Grant Date Fair Value	$ 36.91	$ 46.47	$ 42.15
Vested, Weighted Average Grant Date Fair Value		$ 45.21	$ 48.46
Forfeited, Weighted Average Grant Date Fair Value	$ 43.28	$ 34.16	$ 44.97
Outstanding, end of period, Weighted Average Grant Date Fair Value	$ 39.97	$ 45.37	$ 39.62
Time-Based Restricted Stock Units
Schedule of Share based Compensation Arrangements by Share based Payment Award, Equity Instruments, Other Than Options, Restricted Stock Units [Line Items]
Outstanding, beginning of period, Shares	768,529	838,129	700,904
Granted, Shares	174,841	198,957	367,197
Vested, Shares	(137,194)	(230,613)	(118,730)
Forfeited, Shares	(55,339)	(37,944)	(111,242)
Outstanding, end of period, Shares	750,837	768,529	838,129
Performance And Market-Based Restricted Stock Units
Schedule of Share based Compensation Arrangements by Share based Payment Award, Equity Instruments, Other Than Options, Restricted Stock Units [Line Items]
Outstanding, beginning of period, Shares	69,500	101,680	145,635
Granted, Shares	96,150	42,500	41,250
Vested, Shares		(27,059)	(31,558)
Forfeited, Shares	(32,875)	(47,621)	(53,647)
Outstanding, end of period, Shares	132,775	69,500	101,680