Stockholders' Equity (Summary of Activity Related to Restricted Stock Units) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock Units (RSUs) [Member]
Unvested shares
Outstanding, shares at December 31, 2014	1,200,884
Granted	332,782	504,255	574,017
Forfeited	(47,679)
Vested and issued	(432,165)
Vested and unissued	(46,521)
Outstanding, shares at December 31, 2015	1,007,301	1,200,884
Weighted-Average Grant Date Fair Value Per Share
Outstanding at December 31, 2014	$ 36.06
Granted	45.13	$ 42.54	$ 34.06
Forfeited	40.24
Vested and Issued	34.44
Vested and Unissued	30.93
Outstanding at December 31, 2015	$ 39.74	$ 36.06
Performance Shares [Member]
Unvested shares
Outstanding, shares at December 31, 2014	54,723
Granted	238,690
Outstanding, shares at December 31, 2015	293,413	54,723
Weighted-Average Grant Date Fair Value Per Share
Outstanding at December 31, 2014	$ 42.33
Granted	44.96
Outstanding at December 31, 2015	$ 44.47	$ 42.33