Employee Benefits (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Employer matching contribution, percent	4.00%
Maximum annual contribution per employee, amount	$ 7,200
Defined contribution plan cost recognized	22,900,000	$ 20,000,000	$ 17,400,000
Compensation expense related to deferred compensation plan	100,000	500,000	600,000
Expected future benefit payments, in 2017	1,400,000
Expected future benefit payments, in 2018	2,000,000
Expected future benefit payments, in 2019	1,100,000
Expected future benefit payments, in 2020	1,500,000
Expected future benefit payments, in 2021	1,500,000
Expected future benefit payments in the five years thereafter	$ 9,500,000
Expected long-term return on assets	2.70%
Contributions by employer	$ 2,400,000
Benefits paid to participants under defined benefit plans	$ 1,640,000	775,000	1,350,000
Weighted average amortization period	13 years
Future amortization of unrecognized gains losses	$ 300,000
Amortization of deferred actuarial losses from AOCL/I	0	0	$ 0
Other assets	7,800,000	7,900,000
Other assets
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation plan assets	38,100,000	34,100,000
Other liabilities
Defined Benefit Plan Disclosure [Line Items]
Deferred compensation liability	$ 43,100,000	$ 39,100,000