Incentive Plan - Summary of Stock Options Outstanding (Detail)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Options Outstanding | shares	2,340,842
Weighted Average Remaining Contractual Life, Options Outstanding	5 years 11 days
Weighted Average Exercise Price, Options Outstanding	$ 18.25
Number Of Options Exercisable | shares	1,604,576
Weighted Average Remaining Contractual Life, Options Exercisable	3 years 9 months 27 days
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 15.90
Exercise Prices 8.45 to 12.28
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	8.45
Exercise Prices Higher Limit	$ 12.28
Number of Options Outstanding | shares	465,666
Weighted Average Remaining Contractual Life, Options Outstanding	1 year 8 months 29 days
Weighted Average Exercise Price, Options Outstanding	$ 9.82
Number Of Options Exercisable | shares	465,666
Weighted Average Remaining Contractual Life, Options Exercisable	1 year 8 months 29 days
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 9.82
Exercise Prices From 12.40 to 15.34
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	12.4
Exercise Prices Higher Limit	$ 15.34
Number of Options Outstanding | shares	561,821
Weighted Average Remaining Contractual Life, Options Outstanding	3 years 4 months
Weighted Average Exercise Price, Options Outstanding	$ 14.07
Number Of Options Exercisable | shares	554,321
Weighted Average Remaining Contractual Life, Options Exercisable	3 years 3 months 16 days
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 14.09
Exercise Prices From 16.06 to 18.09
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	16.06
Exercise Prices Higher Limit	$ 18.09
Number of Options Outstanding | shares	590,073
Weighted Average Remaining Contractual Life, Options Outstanding	6 years 3 months 15 days
Weighted Average Exercise Price, Options Outstanding	$ 17.43
Number Of Options Exercisable | shares	271,674
Weighted Average Remaining Contractual Life, Options Exercisable	5 years 11 months 9 days
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 17.50
Exercise Prices From 19.05 to 27.45
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	19.05
Exercise Prices Higher Limit	$ 27.45
Number of Options Outstanding | shares	394,912
Weighted Average Remaining Contractual Life, Options Outstanding	6 years 9 months 29 days
Weighted Average Exercise Price, Options Outstanding	$ 26.40
Number Of Options Exercisable | shares	244,665
Weighted Average Remaining Contractual Life, Options Exercisable	5 years 5 months 13 days
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 26.10
Exercise Prices From 29.01 to 33.28
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Prices Lower Limit	29.01
Exercise Prices Higher Limit	$ 33.28
Number of Options Outstanding | shares	328,370
Weighted Average Remaining Contractual Life, Options Outstanding	8 years 1 month 30 days
Weighted Average Exercise Price, Options Outstanding	$ 29.03
Number Of Options Exercisable | shares	68,250
Weighted Average Remaining Contractual Life, Options Exercisable	8 years 10 days
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 29.10