Stockholders' Equity (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Feb. 12, 2020
Treasury Stock, Shares, Acquired	213,578	218,531	181,642
Treasury Stock Acquired, Average Cost Per Share	$ 25.14	$ 38.66	$ 50.37
Stock Repurchase Program, Authorized Amount				$ 200,000,000
Stock Repurchased and Retired During Period, Shares	1,953,711	3,987,945	5,849,234
Stock Repurchased and Retired During Period, Value	$ 70,000,000	$ 154,516,000	$ 306,393,000
Stock Repurchase and Retired During Period, Weighted Average Price	$ 35.83	$ 38.75	$ 52.38
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 200,000,000.0