Annual report pursuant to Section 13 and 15(d)

Retirement Plans - Additional Information (Detail)

v3.8.0.1
Retirement Plans - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan, new plan effective date 2014-01    
Contribution Plan [Member]      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan minimum eligible period Have completed one month of service.    
Defined contribution plan, maximum percentage of employee contribution 100.00%    
Defined contribution plan, percentage of employer matching contribution percent of match 50.00%    
Defined contribution plan, employer contribution percentage 8.00%    
Defined contribution plan, maximum annual employer contribution per employee $ 4,000    
Defined contribution plan, matching contributions aggregated $ 733,000 $ 628,000 $ 570,000