Equity and Noncontrolling Interests (Common stock) - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Oct. 31, 2015	Dec. 31, 2014
Equity And Noncontrolling Interests [Line Items]
Repurchased shares of common stock, shares	482,000	0	482,000	0
Stock repurchase program, authorized amount						$ 200,000
Repurchased shares of common stock, aggregate cost	$ 26,712,000		$ 26,712,000
Repurchased shares of common stock, average gross price	$ 55.40		$ 55.40
Common stock, shares authorized	100,000,000		100,000,000			100,000,000
Subsequent Event [Member] | At-The-Market Common Equity Sales Program [Member]
Equity And Noncontrolling Interests [Line Items]
Common stock, shares authorized					4,000,000