Common Stock - Schedule of Changes in Common Stock (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Balance, Shares beginning	35,048,338
Exercise of stock options, Shares	539,183	296,103	512,474
Acquisition of treasury stock, Shares	(1,795,444)
Balance, Shares ending	34,189,599	35,048,338
Balance, beginning	$ (72,114)	$ (62,330)	$ (18,502)
Exercise of stock options	3,744	1,733	3,436
Acquisitions of treasury stock	11,401
Balance, ending	(39,637)	(72,114)	(62,330)
Common Stock [Member]
Class of Stock [Line Items]
Balance, beginning	416	411	406
Exercise of stock options	6	3	5
Settlement of restricted stock units	4	2
Acquisitions of treasury stock	0	0
Balance, ending	$ 426	$ 416	$ 411
Common Stock Outstanding [Member]
Class of Stock [Line Items]
Balance, Shares beginning	35,048,338	34,568,942	34,056,468
Exercise of stock options, Shares	539,183	296,103	512,474
Settlement of restricted stock units, Shares	397,522	183,293
Acquisition of treasury stock, Shares	(1,795,444)
Balance, Shares ending	34,189,599	35,048,338	34,568,942