Stock Options and Other Equity-Based Incentive Instruments - Stock Option Activity (Detail)	9 Months Ended
	Sep. 30, 2016 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Number of Shares, beginning balance | shares	948,350
Options granted, Number of Shares | shares	0
Options exercised, Number of Shares | shares	132,700
Options forfeited, Number of Shares | shares	(6,000)
Options outstanding, Number of Shares, ending balance | shares	809,650
Options outstanding, Weighted Average Exercise Price, beginning balance	$ 17.94
Options granted, Weighted Average Exercise Price	0
Options exercised, Weighted Average Exercise Price	21.91
Options forfeited, Weighted Average Exercise Price	23.21
Options outstanding, Weighted Average Exercise Price, ending balance	17.25
Options granted, Weighted Average Fair Value on Date of Grant	0
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 granted, Option Price per Share	0
Options exercised, Option Price per Share	14.76
Options forfeited, Option Price per Share	23.21
Options outstanding, Option Price per Share, ending balance	12.63
Maximum [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, Option Price per Share, beginning balance	25.91
Options granted, Option Price per Share	0
Options exercised, Option Price per Share	25.91
Options forfeited, Option Price per Share	23.21
Options outstanding, Option Price per Share, ending balance	$ 23.21