Stock-Based Compensation - Shares Issued in Connection with Stock Compensation Awards (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
New shares issued from available authorized shares	0	310,021	0	593,363
Issued from available treasury stock	110,489	0	428,599	158,712
Total	110,489	310,021	428,599	752,075
Proceeds from stock option exercises	$ 6,283	$ 19,402	$ 25,448	$ 44,149