Common Stock and Treasury Stock - Additional Information (Detail) - USD ($)	3 Months Ended	67 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Feb. 28, 2018
Stock authorized to purchase under stock repurchase program			$ 200,000,000
Repurchase of common stock, shares	1,346,427	43,129,393
Repurchase of common stock, value	$ 31,100,000	$ 524,400,000
Maximum [Member]
Remaining value of shares authorized for purchase under the stock repurchase program	$ 200,000,000	$ 200,000,000