Stockholders' Equity (Details Textual) (USD $)	1 Months Ended	3 Months Ended			3 Months Ended	12 Months Ended
	Feb. 28, 2013	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2011 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2010 Restricted Stock Units (RSUs) [Member]	Dec. 31, 2009 Restricted Stock Units (RSUs) [Member]
Stockholders' Equity (Textual) [Abstract]
RSU's issued		264,000		301,000		71,000	63,000	95,496
Performance of RSU's Vesting						100% or 40% on April 1, 2014	100% or 40% on April 1, 2013	100% or 40% on April 1, 2012
Performance of Outstanding RSU's								40.00%
Weighted average grant date fair value for RSUs granted		$ 27.55
Compensation expense Estimate vesting						100.00%	100.00%	100.00%
Modified Estimate vesting of RSU's					0.00%		0.00%	40.00%
Stockholders' Equity (Additional Textual) [Abstract]
Aggregate cost of repurchase of common stock		$ 210,843,000		$ 210,843,000
Dividend declared and paid per share		$ 0.15	$ 0.14
Aggregate dividend declared for the year		3,400,000	3,200,000
Authorized to Purchase of common stock under the stock repurchase program	$ 50,000,000	$ 360,000,000
Cumulative repurchase of common stock		9,200,000