Equity impact of the value of stock that has been repurchased and retired during the period. The excess of the purchase price over par value can be charged against retained earnings (once the excess is fully allocated to additional paid in capital).

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Stock Repurchase Plan (Detail) - USD ($)	12 Months Ended
Stock Repurchase Plan (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 26, 2016	Feb. 26, 2015
Equity, Class of Treasury Stock [Line Items]
Stock repurchased and canceled (in shares)		0
Stock repurchased and canceled	$ 100,000,000		$ 24,234,000
2015 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase plan (up to)					$ 100,000,000
Stock repurchased and canceled (in shares)			400,500
Stock repurchased and canceled			$ 24,200,000
2016 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase plan (up to)				$ 100,000,000
Stock repurchased and canceled (in shares)	1,991,206
Stock repurchased and canceled	$ 100,000,000