Stock Options and Other Equity-Based Incentive Instruments - Stock Option Activity (Detail)	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Number of Shares, beginning balance | shares	343,000
Options exercised, Number of Shares | shares	(157,000)
Options outstanding, Number of Shares, ending balance | shares	186,000
Options outstanding, Weighted Average Exercise Price, beginning balance	$ 16.67
Options exercised, Weighted Average Exercise Price	15.92
Options outstanding, Weighted Average Exercise Price, ending balance	17.45
Minimum [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Option Price per Share, beginning balance	12.63
Options exercised, Option Price per Share	12.63
Options outstanding, Option Price per Share, ending balance	14.54
Maximum [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Option Price per Share, beginning balance	23.21
Options exercised, Option Price per Share	19.46
Options outstanding, Option Price per Share, ending balance	$ 23.21