Stock-Based Compensation Plans (Details 4) (Restricted stock [Member], USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Restricted stock [Member]
Stock-based compensation expense
Number of Restricted Shares, Beginning balance	957,711	1,244,864	1,034,139
Number of Restricted Shares, Granted	206,965	435,548	549,264
Number of Restricted Shares, Performance share pay-out	91,498	130,552	206,664
Number of Restricted Shares, Canceled	(7,390)	(279,081)	(71,152)
Number of Restricted Shares, Vested	(459,474)	(574,172)	(474,051)
Number of Restricted Shares, Ending balance	789,310	957,711	1,244,864
Weighted Average Grant Date Fair Value, Beginning balance	$ 15.69	$ 11.23	$ 9.64
Weighted Average Grant Date Fair Value, Ending balance	$ 21.88	$ 15.69	$ 11.23