Earnings Per Share - Shares Repurchased (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended	118 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2021
Schedule Of Shares Repurchased [Line Items]
Total Cost of Shares Repurchased	$ 13,019	$ 22,909	$ 35,928
Minimum [Member]
Schedule Of Shares Repurchased [Line Items]
Range of Prices Paid Per Share	$ 23.90		$ 23.33
Maximum [Member]
Schedule Of Shares Repurchased [Line Items]
Range of Prices Paid Per Share	$ 27.94		$ 31.91
2011 Share Repurchase Program [Member]
Schedule Of Shares Repurchased [Line Items]
Total Number of Shares Repurchased	500		1,360	8,300