Benefit Plans - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Stock Option Activity [Line Items]
Weighted Average Exercise Price, Beginning balance	$ 24.77	$ 25.70	$ 25.35
Weighted Average Exercise Price, Granted	$ 16.61	$ 16.91	$ 13.87
Weighted Average Exercise Price, Exercised	$ 10.02	$ 9.25	$ 6.54
Weighted Average Exercise Price, Forfeited	$ 33.40	$ 28.10	$ 26.21
Weighted Average Exercise Price, Ending balance	$ 22.48	$ 24.77	$ 25.70
Weighted Average Exercise Price, Options exercisable	$ 25.75	$ 27.53	$ 29.12
Weighted-Average Remaining Contractual Term (Years), Ending Balance	5 years 7 months 6 days
Weighted-Average Remaining Contractual Term (Years), Options exercisable	4 years	4 years 1 month 6 days	4 years 6 months
Aggregate Intrinsic Value, Ending balance	$ 11,088
Aggregate Intrinsic Value, Options exercisable	$ 9,077	$ 6,491	$ 6,538
Employees [Member]
Schedule Of Stock Option Activity [Line Items]
Number of Options Outstanding, Beginning Balance	2,661	2,596	2,683
Number of Options, Granted	774	345	345
Number of Options, Exercised	(154)	(87)	(266)
Number of Options, Forfeited	(320)	(193)	(166)
Number of Options Outstanding, Ending Balance	2,961	2,661	2,596
Number of Options exercisable	1,922	2,052	2,035
Directors [Member]
Schedule Of Stock Option Activity [Line Items]
Number of Options Outstanding, Beginning Balance	0	0	10
Number of Options, Granted	0	0	0
Number of Options, Exercised	0	0	0
Number of Options, Forfeited	0	0	(10)
Number of Options Outstanding, Ending Balance	0	0	0
Number of Options exercisable	0	0	0