Share-Based Compensation - Additional Information (Detail) - USD ($)					3 Months Ended		9 Months Ended
	May 19, 2020	Apr. 01, 2020	Feb. 25, 2020	May 15, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Number of stock options granted to employees (in shares)					147,000	292,500	1,865,950	1,290,475
Vesting period (in years)							4 years
Options outstanding (in shares)					8,795,230		8,795,230		7,008,403
Weighted average exercise price (in dollars per share)					$ 20.97		$ 20.97		$ 23.34
Share-based compensation cost not yet recognized, Stock Options					$ 36,800,000		$ 36,800,000
Expected recognition period of share-based compensation not yet recognized							2 years 5 months 23 days
Stock Option
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Tax benefit from compensation expense					1,100,000	$ 1,200,000	$ 3,300,000	$ 3,600,000
Intrinsic value of options exercised					$ 59,000	$ 0	$ 94,000	$ 109,000
2018 Long Term Incentive Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Number of additional shares authorized (in shares)	1,500,000			1,177,933
Authorized shares for issuance (in shares)				3,300,000
Maximum number of shares to be issued - ISO exercise (in shares)					2,500,000		2,500,000
Grant period				10 years			10 years
Number of shares available for grant (in shares)					1,389,154		1,389,154
2012 Long Term Incentive Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Grant period							10 years
2020 Employment Inducement Incentive Plan
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Number of additional shares authorized (in shares)		120,000			120,000
Authorized shares for issuance (in shares)					480,000		480,000
Grant period			10 years
Number of shares available for grant (in shares)					0		0