Common Stock and Senior Convertible Preferred Stock - Schedule of Changes in Senior Convertible Preferred Stock, Common Stock and Treasury Stock (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity [Abstract]
Senior Convertible Preferred Stock, balance at beginning and end of year	0	0	0
Common Stock, balance at beginning of year	23,321,087	23,029,000	22,384,000
Common Stock, issued for employee stock plans	367,000	292,000	645,000
Common Stock, balance at end of year	23,688,347	23,321,087	23,029,000
Treasury Stock, balance at beginning of year	(2,515,925)	(2,480,000)	(1,606,000)
Treasury Stock, shares repurchased	(74,000)	(36,000)	(874,000)
Treasury Stock, balance at end of year	(2,589,803)	(2,515,925)	(2,480,000)