Share-Based Compensation Plans - Stock activity - RSUs, PSUs, MSUs (Details) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Nonvested share activity [Rollforward]
Options Exercised (shares)	(149,700)
Weighted-average grant-date fair value [Rollforward]
Options Exercised - Exercise Price (in dollars per share)	$ 25.20
Restricted Stock Units
Nonvested share activity [Rollforward]
Nonvested beginning balance (shares)	367,100
Granted (shares)	144,700
Cancelled (shares)	(57,200)
Vested (shares)	(181,600)
Nonvested ending balance (shares)	273,000	367,100
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance (in dollars per share)	$ 25.87
Granted (in dollars per share)	27.09
Cancelled (in dollars per share)	26.05
Vested (in dollars per share)	26.37
Nonvested ending balance (in dollars per share)	$ 26.16	$ 25.87
Market Share Units MSU
Nonvested share activity [Rollforward]
Nonvested beginning balance (shares)	163,300
Granted (shares)	108,600
Cancelled (shares)	(13,100)
Nonvested ending balance (shares)	258,800	163,300
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance (in dollars per share)	$ 25.47
Granted (in dollars per share)	30.37
Cancelled (in dollars per share)	27.86
Nonvested ending balance (in dollars per share)	$ 27.40	$ 25.47
Stock Options
Nonvested share activity [Rollforward]
Nonvested beginning balance (shares)	844,800
Cancelled (shares)	(6,800)
Options Exercised (shares)	(149,700)
Nonvested ending balance (shares)	688,300	844,800
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance (in dollars per share)	$ 5.83
Cancelled (in dollars per share)	1.75
Options Exercised - Exercise Price (in dollars per share)	3.96
Nonvested ending balance (in dollars per share)	$ 6.28	$ 5.83
Performance Shares PSU
Nonvested share activity [Rollforward]
Nonvested beginning balance (shares)	343,600
Granted (shares)	199,100
Cancelled (shares)	(39,300)
Nonvested ending balance (shares)	503,400	343,600
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance (in dollars per share)	$ 24.06
Granted (in dollars per share)	29.10
Cancelled (in dollars per share)	25.69
Nonvested ending balance (in dollars per share)	$ 25.93	$ 24.06
Deferred Stock Units
Nonvested share activity [Rollforward]
Nonvested beginning balance (shares)	28,300
Granted (shares)	21,400
Vested (shares)	(28,300)
Nonvested ending balance (shares)	21,400	28,300
Weighted-average grant-date fair value [Rollforward]
Nonvested beginning balance (in dollars per share)	$ 24.70	$ 26.80
Granted (in dollars per share)	32.79
Vested (in dollars per share)	24.70
Nonvested ending balance (in dollars per share)	$ 32.79	$ 24.70