Summary of Significant Accounting Policies (Details Textual) - Equity Component [Domain]	3 Months Ended			6 Months Ended
	Jun. 30, 2015 USD ($) $ / shares shares		Jun. 30, 2014 USD ($) shares	Jun. 30, 2015 USD ($) customer $ / shares shares		Jun. 30, 2014 USD ($) shares	Apr. 30, 2015 $ / shares shares	Dec. 31, 2014 shares
Summary of Significant Accounting Policies (Textual) [Abstract]
Authorized amount from board of directors for share repurchase | $	$ 250,000,000			$ 250,000,000
Share repurchase program expiry date				Dec. 31, 2015
Shares repurchased under the program (in shares)	1,669,764		63,600	2,390,804		340,146
Cost of shares repurchased | $	$ 50,000,000		$ 2,500,000	$ 75,000,000		$ 12,500,000
Common stock, shares authorized	400,000,000	[1]		400,000,000	[1]		200,000,000	200,000,000
Common stock, par value per share | $ / shares	$ 0.01			$ 0.01			$ 1.00
Customer receivables concentration | Net receivable | Rail Group
Summary of Significant Accounting Policies (Textual) [Abstract]
Number of customers | customer				1
Net receivables percentage				11.00%

[1] (unaudited)