Schedule of Selected Quarterly Financial Information (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Quarterly Financial Information [Line Items]
Revenue	$ 431,103	[1]	$ 421,466	[1]	$ 425,005	[1]	$ 416,723	[1]	$ 427,677	[1]	$ 435,727	[1]	$ 433,897	[1]	$ 426,356	[1]	$ 1,694,297	$ 1,723,657	$ 1,688,805
Operating income	56,019	[1]	67,271	[1]	67,969	[1]	59,892	[1]	80,299	[1]	79,733	[1]	75,125	[1]	69,451	[1]	251,151	304,608	331,741
(Loss) income from discontinued operations, net of taxes			(663)	[1]	(2,739)	[1]	(355)	[1]	150	[1]	99	[1]	(150)	[1]	(304)	[1]	(3,757)	(205)	180
Net income	47,471	[1]	51,843	[1]	20,429	[1]	181,092	[1]	45,408		42,339		37,334		31,680		300,835	156,761	162,510
Basic earnings per share: Net income	$ 0.41	[2]	$ 0.45	[2]	$ 0.19	[2]	$ 1.81	[2]	$ 0.46		$ 0.42		$ 0.37		$ 0.32		$ 2.74	$ 1.58	$ 1.55
Diluted earnings per share: Net income	$ 0.41	[2]	$ 0.44	[2]	$ 0.19	[2]	$ 1.78	[2]	$ 0.45		$ 0.42		$ 0.37		$ 0.32		$ 2.70	$ 1.56	$ 1.54
Discontinued operations - revenue					(8,976)		(9,001)		(9,184)		(9,126)		(8,969)		(8,949)		(19,984)	(36,421)	(46,808)
Discontinued operations - Operating Income					4,359		560		(217)		(155)		240		(93)		(5,981)	(443)	314
Discontinued operations subsequent to the respective reporting period					(2,739)		(355)		150		99		(150)		58
Revised loss from discontinued operations, net of taxes			(663)	[1]	(2,739)	[1]	(355)	[1]	150	[1]	99	[1]	(150)	[1]	(304)	[1]	(3,757)	(205)	180
Previously Reported
Quarterly Financial Information [Line Items]
Revenue					433,981		425,724		436,861		444,853		442,866		435,305
Operating income					63,610		59,332		80,516		79,888		74,885		69,544
Discontinued Operation
Quarterly Financial Information [Line Items]
(Loss) income from discontinued operations, net of taxes															(362)
Revised loss from discontinued operations, net of taxes															$ (362)

[1] The amounts presented for the first two quarters of 2013 and the four quarters of 2012 are not equal to the same amounts previously reported in the respective reports on Form 10-Q and Form 10-K for each period as a result of discontinued operations. Below is a reconciliation to the previously reported amounts in Form 10-Q.

[2] The earnings per share amounts in the first quarter of 2013 were favorably impacted by the net tax benefit resulting from the revaluation of certain deferred tax assets and liabilities associated with the REIT conversion effective January 1, 2013. Additionally, the earnings per share amounts in the second quarter of 2013 were negatively impacted by $36.3 million of expenses associated with debt refinancing transactions.