Stock-Based Compensation - Shares Issued in Connection with Stock Compensation Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
New shares issued from available authorized shares	0	9,299	0	602,662
Issued from available treasury stock	19,232	13,425	447,831	172,137
Total	19,232	22,724	447,831	774,799
Proceeds from stock option exercises	$ 1,119	$ 1,274	$ 26,567	$ 45,422