Employee Benefits (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent	4.00%
Maximum annual contribution per employee, Amount	$ 7,000
Defined contribution plan cost recognized	17,400,000		15,800,000		14,200,000
Compensation expense related to deferred compensation plan	600,000		400,000		400,000
Expected future benefit payments in 2015	1,000,000
Expected future benefit payments, in 2016	1,900,000
Expected future benefit payments, in 2017	1,400,000
Expected future benefit payments, in 2018	1,400,000
Expected future benefit payments, in 2019	1,400,000
Expected future benefit payments in the five years thereafter	9,600,000
Expected long-term return on assets	2.70%
Contributions by employer	2,800,000
Benefits paid to participants under defined benefit plans	(1,350,000)	[1]	(1,255,000)	[1]	(680,000)	[1]
Other assets	8,500,000
Weighted average amortization period	14 years
Future amortization of unrecognized gains losses	400,000
Actual amortization of deferred actuarial losses (gains) from AOCI to pension expense (less than $0.1 million for 2014 and 2013, less then $0.2 million in 2012)	100,000		100,000		(200,000)
Other assets
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation plan assets	34,700,000		32,600,000
Other liabilities
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation liability	$ 39,100,000		$ 36,400,000

[1] The Company projects the following approximate amounts will be paid in future years to plan participants: $1.0 million in 2015; $1.9 million in 2016; $1.4 million in each of the years 2017, 2018, and 2019; and $9.6 million in total in the five years thereafter.