Common Stock and Treasury Stock - Additional Information (Details) - USD ($)	3 Months Ended	6 Months Ended		175 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Feb. 28, 2018
Equity [Abstract]
Stock repurchase program, amount approved for repurchase					$ 200,000,000.0
Stock repurchase program, shares repurchased, shares	1,000,000	23,802	2,346,427	44,153,195
Stock repurchase program, shares repurchased, value	$ 23,414,000	$ 631,000	$ 54,527,000	$ 548,500,000
Stock repurchase program, maximum remaining amount authorized for purchase		$ 176,000,000.0		$ 176,000,000.0