Share-Based Compensation - Summary of Liability Based Award Activity (Details) (Liability Based Awards, USD $)	3 Months Ended
	Mar. 31, 2014
Performance unit incentive plan (PUP)
Summary of Liability-Based Award Activity [Roll Forward]
Beginning Balance, Shares	299,768
Granted, Shares	123,300
Vested, Shares	(94,600)
Forfeited or Cancelled, Shares	0
Ending Balance, Shares	328,468
Beginning Balance, Weighted-Average Grant Date Fair Value	$ 23.46
Granted, Weighted-Average Grant Date Fair Value	$ 23.71
Vested, Weighted-Average Grant Date Fair Value	$ 23.01
Forfeited or Cancelled, Weighted-Average Grant Date Fair Value	$ 0.00
Ending Balance, Weighted-Average Grant Date Fair Value	$ 23.69
Restricted Stock (RSU)
Summary of Liability-Based Award Activity [Roll Forward]
Beginning Balance, Shares	430,899
Granted, Shares	83,300
Vested, Shares	(132,255)
Forfeited or Cancelled, Shares	(5,140)
Ending Balance, Shares	376,804
Beginning Balance, Weighted-Average Grant Date Fair Value	$ 22.78
Granted, Weighted-Average Grant Date Fair Value	$ 23.95
Vested, Weighted-Average Grant Date Fair Value	$ 22.67
Forfeited or Cancelled, Weighted-Average Grant Date Fair Value	$ 22.44
Ending Balance, Weighted-Average Grant Date Fair Value	$ 23.09
Performance Based Restricted Stock Shares (PBRSU)
Summary of Liability-Based Award Activity [Roll Forward]
Beginning Balance, Shares	28,560
Granted, Shares	6,700
Vested, Shares	(9,890)
Forfeited or Cancelled, Shares	0
Ending Balance, Shares	25,370
Beginning Balance, Weighted-Average Grant Date Fair Value	$ 22.91
Granted, Weighted-Average Grant Date Fair Value	$ 24.95
Vested, Weighted-Average Grant Date Fair Value	$ 23.45
Forfeited or Cancelled, Weighted-Average Grant Date Fair Value	$ 0.00
Ending Balance, Weighted-Average Grant Date Fair Value	$ 23.24