Employee Benefit Plans - Awards Activity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Options [Member]
Summary of options issued and outstanding
Balance at the beginning of the period (in shares)	3,129,251
Options granted (in shares)	83,162
Options exercised (in shares)	(409,560)
Options forfeited/expired (in shares)	0
Balance at the end of the period (in shares)	2,802,853	3,129,251
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 20.97
Options granted (in dollars per share)	$ 21.88
Options exercised (in dollars per share)	$ 17.88
Options forfeited (in dollars per share)	$ 0.00
Balance at the end of the period (in dollars per share)	$ 21.45	$ 20.97
Weighted Average Grant Date Fair Value (in dollars per share)	$ 10.35	$ 8.94	$ 8.62
Number of Exercisable Options (in shares)	2,631,653	2,987,088
Performance Stock Options [Member]
Summary of options issued and outstanding
Balance at the beginning of the period (in shares)	365,717
Options granted (in shares)	0
Options exercised (in shares)	0
Options forfeited/expired (in shares)	(118,838)
Balance at the end of the period (in shares)	246,879	365,717
Weighted Average Exercise Price
Balance at the beginning of the period (in dollars per share)	$ 17.80
Options granted (in dollars per share)	$ 0.00
Options exercised (in dollars per share)	$ 0.00
Options forfeited (in dollars per share)	$ 17.44
Balance at the end of the period (in dollars per share)	$ 17.97	$ 17.80
Weighted Average Grant Date Fair Value (in dollars per share)	$ 0.00	$ 8.17	$ 7.84
Number of Exercisable Options (in shares)	0	0
Restricted Stock Awards [Member]
Restricted Stock Award and Restricted Stock Unit Activity
Nonvested at the beginning of the period (in shares)	48,273
Granted (in shares)	47,747
Vested (in shares)	(48,273)
Forfeited (in shares)	(4,170)
Nonvested at the end of the period (in shares)	43,577
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 23.20
Granted (in dollars per share)	$ 23.98
Vested (in dollars per share)	$ 23.20
Forfeited (in dollars per share)	$ 23.98
Nonvested at the end of the period (in dollars per share)	$ 23.98
Restricted Stock Units [Member]
Restricted Stock Award and Restricted Stock Unit Activity
Nonvested at the beginning of the period (in shares)	736,409
Granted (in shares)	238,976
Vested (in shares)	(284,082)
Forfeited (in shares)	0
Nonvested at the end of the period (in shares)	691,303
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 17.63
Granted (in dollars per share)	$ 21.61
Vested (in dollars per share)	$ 17.13
Forfeited (in dollars per share)	$ 0.00
Nonvested at the end of the period (in dollars per share)	$ 19.23
Performance Restricted Stock Units [Member]
Restricted Stock Award and Restricted Stock Unit Activity
Nonvested at the beginning of the period (in shares)	223,410
Granted (in shares)	203,287
Vested (in shares)	0
Forfeited (in shares)	(3,395)
Nonvested at the end of the period (in shares)	423,302
Weighted Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)	$ 27.79
Granted (in dollars per share)	$ 25.17
Vested (in dollars per share)	$ 0.00
Forfeited (in dollars per share)	$ 27.35
Nonvested at the end of the period (in dollars per share)	$ 26.72