Earnings Per Share - Shares Repurchased (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	6 Months Ended	94 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jun. 30, 2019
Schedule Of Shares Repurchased [Line Items]
Total Cost of Shares Repurchased	$ 20,178	$ 20,178
Minimum [Member]
Schedule Of Shares Repurchased [Line Items]
Range of Prices Paid Per Share	$ 24.72	$ 24.72
Maximum [Member]
Schedule Of Shares Repurchased [Line Items]
Range of Prices Paid Per Share	$ 27.30	$ 27.30
2011 Share Repurchase Program [Member]
Schedule Of Shares Repurchased [Line Items]
Total Number of Shares Repurchased	771	771	6,000