Stock-based Compensation (Details) (USD $)	3 Months Ended		3 Months Ended			0 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Stock option plans	Mar. 31, 2013 Restricted stock units	Mar. 31, 2012 Restricted stock units	Mar. 26, 2013 Restricted stock units Members of management	Mar. 26, 2013 Restricted stock units Members of management Requisite service period of one year	Mar. 26, 2013 Restricted stock units Members of management Requisite service period of two years	Mar. 26, 2013 Restricted stock units Members of management Requisite service period of three years	Mar. 26, 2013 Restricted stock units Members of management Minimum	Mar. 26, 2013 Restricted stock units Members of management Maximum	Mar. 31, 2013 DSUs Directors	Dec. 31, 2012 DSUs Directors
Stock-based Compensation
Shares authorized for repurchase under stock repurchase plan	895,655
Number of shares held in treasury	1,595,973	1,616,282
Shares
Outstanding at beginning of year (in shares)			857,468
Forfeited (in shares)			148,689
Outstanding at end of period (in shares)			708,779
Exercisable at end of period (in shares)			708,779
Weighted-Average Exercise Price
Outstanding at beginning of year (in dollars per share)			$ 17.01
Forfeited (in dollars per share)			$ 16.00
Outstanding at end of period (in dollars per share)			$ 17.22
Exercisable at end of period (in dollars per share)			$ 17.22
Weighted-Average Remaining Contractual Term
Outstanding at end of period			2 years 9 months 14 days
Exercisable at end of period			2 years 9 months 14 days
Shares
Non-vested at beginning of year (in shares)	769,403			736,412								32,991	32,991
Granted (in shares)	13,158			13,158		13,158
Vested (in shares)	(18,648)			(18,648)
Non-vested at end of period (in shares)	763,913			730,922			4,386	4,386	4,386			32,991	32,991
Outstanding at end of period (in shares)	787,842			730,922								56,920
Weighted-Average Grant Date Fair Value
Non-vested at beginning of year (in dollars per share)	$ 4.92
Granted (in dollars per share)	$ 4.56
Vested (in dollars per share)	$ 5.24
Non-vested at end of period (in dollars per share)	$ 4.90
Outstanding at end of period (in dollars per share)	$ 4.91
Additional disclosures
Stock price (in dollars per share)						$ 4.56
Amount of compensation cost to be recognized				$ 2,000,000		$ 60,000
Requisite service period							1 year	2 years	3 years
Vesting rights of shares granted (as a percent)						100.00%
Period over which cost will be recognized				2 years 8 months 12 days						1 year	3 years
Compensation expense recognized				$ 300,000	$ 200,000