Summary of Stock Option Transactions Relating to Non-Qualified Stock Option Plans (Detail) - Stock options $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Number of Shares
No. of options, Outstanding at December 31, 2017 | shares	1,014
No. of options, Granted | shares	0
No. of options, Exercised | shares	(147)
No. of options, Cancelled | shares	(161)
No. of options, Outstanding at December 31, 2018 | shares	706
No. of options, Exercisable at December 31, 2018 | shares	706
Weighted-Average Exercise Price per Share
Weighted-Average Exercise Price of options, Outstanding at December 31, 2017 | $ / shares	$ 20.03
Weighted-Average Exercise Price of options, Granted | $ / shares	0
Weighted-Average Exercise Price of options, Exercised | $ / shares	16.16
Weighted-Average Exercise Price of options, Cancelled | $ / shares	22.25
Weighted-Average Exercise Price of options, Outstanding at December 31, 2018 | $ / shares	20.32
Weighted-Average Exercise Price of options, Exercisable at December 31, 2018 | $ / shares	$ 20.32
Weighted Average Remaining Contractual Term (in years)
Outstanding at December 31, 2018	2 years 3 months 18 days
Exercisable at December 31, 2018	2 years 3 months 18 days
Aggregate Intrinsic Value
Outstanding at December 31, 2018 | $	$ 267
Exercisable at December 31, 2018 | $	$ 267