Employee Benefits - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Installment $ / shares shares	Dec. 31, 2015 USD ($) Installment $ / shares shares	Dec. 31, 2014 USD ($)
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Healthcare benefit expense, net of employee contributions	$ 15,200,000	$ 11,800,000	$ 8,100,000
Accrued compensation	18,212,000	14,488,000
Workers' compensation expense	12,100,000	12,000,000	9,800,000
Administration expense related to employee contribution plan	1,300,000	$ 800,000	$ 700,000
Unrecognized compensation expense	$ 3,100,000
Common nonvested shares, compensation cost not yet recognized, period for recognition	2 years 2 months 12 days
2014 Omnibus Incentive Plan [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Common stock granted, shares | shares	100,000	100,000
Share based compensation expenses	$ 1,600,000	$ 1,800,000
Number of equal installments for vesting common stock | Installment	3,000,000	3,000,000
Number of shares surrendered to satisfy tax withholding obligations | shares	32,000
Share based compensation, recognized tax benefits	$ 300,000	$ 0
Common stock shares available for issuance | shares	2,700,000
Common stock shares authorized | shares	3,000,000
2014 Omnibus Incentive Plan [Member] | Directors [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Common stock granted, shares | shares	9,000	13,000
Grant date fair value for restricted stock granted | $ / shares	$ 34.23	$ 22.74
Share based compensation expenses	$ 300,000	$ 300,000
Medical IBNR Included in Accrued Compensation [Member]
Pension Plans, Postretirement and Other Employee Benefits [Line Items]
Accrued compensation	$ 1,700,000	$ 1,500,000