Shareholders' Equity - Schedule of Company's Common Stock Repurchases Made on Open Market (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Equity, Class of Treasury Stock [Line Items]
Total Number of Shares Repurchased	1,079,005
Open Market Purchases of Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Average Price Paid Per Share	$ 82.25	$ 68.45
Total Number of Shares Repurchased	1,079,000	4,869,000
Dollar Value of Shares Repurchased	$ 88,744	$ 333,328