Shareholders' Equity (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Number of shares authorized to be repurchased	7,100,000
Purchase of treasury stock	$ 2,800,000	$ 0
Treasury Stock Acquired, Average Cost Per Share	$ 56.78
Shares issued	1,500,000
Common stock reissued	300,000