Benefit Plans - Summary of Company's Option Activity (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Options, Beginning Balance	1,343,760	1,772,062	2,838,553
Number of Options, granted	456,200	203,600	192,800
Number of Options, exercised	(270,650)	(612,682)	(1,237,341)
Number of Options, cancelled/forfeited/expired	(118,660)	(19,220)	(21,950)
Number of Options, Ending Balance	1,410,650	1,343,760	1,772,062
Number of Options, Exercisable at December 31, 2015	662,345
Number of Options, Expected to Vest after December 31, 2015	673,475
Weighted-Average Price, Beginning Balance	$ 27.25	$ 24.68	$ 24.37
Weighted-Average Price, Options granted	31.69	32.79	29.14
Weighted-Average Price, Options exercised	19.81	21.55	24.71
Weighted-Average Price, Options cancelled/forfeited/expired	29.58	30.35	25.20
Weighted-Average Price, Ending Balance	29.91	$ 27.25	$ 24.68
Weighted-Average Price, Exercisable at December 31, 2015	27.53
Weighted-Average Price, Expected to Vest after December 31, 2015	$ 31.64
Weighted-Average Remaining Contractual Term, Balance At December 31, 2015	3 years 9 months 26 days
Weighted-Average Remaining Contractual Term, Exercisable at December 31, 2015	1 year 10 months 21 days
Weighted-Average Remaining Contractual Term, Expected to Vest after December 31, 2015	5 years 6 months 11 days
Aggregate Intrinsic Value, Balance At December 31, 2015	$ (6.6)
Aggregate Intrinsic Value, Exercisable at December 31, 2015	(1.5)
Aggregate Intrinsic Value, Expected to Vest after December 31, 2015	$ (4.3)