Stockholders' Equity (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 14, 2018	Nov. 15, 2017	Oct. 17, 2016
Treasury Stock, Shares, Acquired	181,642	188,870	141,358
Treasury Stock Acquired, Average Cost Per Share	$ 50.37	$ 50.17	$ 37.5854214123
Stock Repurchase Program, Authorized Amount				$ 350,000,000	$ 150,000,000	$ 400,000,000
Stock Repurchased and Retired During Period, Shares	5,849,234	2,081,227	652,835
Stock Repurchased and Retired During Period, Value	$ 306,400,000	$ 99,700,000	$ 27,900,000
Stock Repurchase and Retired During Period, Weighted Average Price	$ 52.38	$ 47.89	$ 42.78
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 110,100,000