Employee Benefit, Retirement, and Deferred Compensation Plans - Additional Information, Defined Contribution Plans (Detail) - 401 (k) Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Contribution Plan Disclosure [Line Items]
Contribution made to consolidated defined contribution plan	$ 3.7	$ 3.0	$ 2.4
Employer Matching Contribution Tranche One [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan employee matching contribution	100.00%
Percentage of contribution based on participant's age and ranges	1.00%
Employer Matching Contribution Tranche Two [Member]
Defined Contribution Plan Disclosure [Line Items]
Defined contribution plan employee matching contribution	50.00%
Minimum [Member] | Employer Matching Contribution Tranche Two [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of contribution based on participant's age and ranges	1.00%
Maximum [Member] | Employer Matching Contribution Tranche Two [Member]
Defined Contribution Plan Disclosure [Line Items]
Percentage of contribution based on participant's age and ranges	6.00%