Business Segment Information - Reconciliation of Segment Income from Operations to Income before Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting [Abstract]
Total segment income from operations	$ 121,923	$ 147,635	$ 267,277	$ 301,725
Interest and other debt expense	17,159	19,276	50,364	58,394
Income before income taxes	$ 104,764	$ 128,359	$ 216,913	$ 243,331