Stock Based Compensation - Summary of Restricted Shares Activity (Details) - $ / shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock
Number of Shares
Non-vested shares at beginning of year (in shares)		346,924	225,687	79,335
Granted (in shares)		259,677	291,368	208,715
Vested (in shares)		(181,812)	(126,073)	(55,571)
Canceled (in shares)	[1]	(5,494)	(44,058)	(6,792)
Non-vested shares at end of year (in shares)		419,295	346,924	225,687
Weighted Avg Grant Date Fair Value
Weighted Average Grant Date Fair Value, Non-vested shares at beginning of year (in USD per share)		$ 16.91	$ 23.65	$ 24.84
Weighted Average Grant Date Fair Value, Granted (in USD per share)		18.14	14.14	23.11
Weighted Average Grant Date Fair Value, Vested (in USD per share)		17.62	21.81	23.24
Weighted Average Grant Date Fair Value, Canceled (in USD per share)	[1]	16.23	19.06	24.28
Weighted Average Grant Date Fair Value, Non-vested shares at end of year (in USD per share)		$ 17.38	$ 16.91	$ 23.65
Performance-Based Restricted Stock
Number of Shares
Non-vested shares at beginning of year (in shares)		655,133	480,757	506,846
Granted (in shares)		553,909	566,092	284,809
Vested (in shares)		(147,477)	(190,977)	(154,467)
Canceled (in shares)	[2]	(349,000)	(200,739)	(156,431)
Non-vested shares at end of year (in shares)		712,565	655,133	480,757
Weighted Avg Grant Date Fair Value
Weighted Average Grant Date Fair Value, Non-vested shares at beginning of year (in USD per share)		$ 17.81	$ 24.18	$ 23.84
Weighted Average Grant Date Fair Value, Granted (in USD per share)		18.00	13.88	23.50
Weighted Average Grant Date Fair Value, Vested (in USD per share)		21.49	20.58	19.58
Weighted Average Grant Date Fair Value, Canceled (in USD per share)	[2]	19.55	23.38	28.86
Weighted Average Grant Date Fair Value, Non-vested shares at end of year (in USD per share)		$ 17.01	$ 17.81	$ 24.18

[1] (1) Represents shares that were canceled as result of terminations of employment.

[2] (1) Represents shares that were canceled as a result of achievement of performance targets as outlined in the respective grant agreement at below the maximum levels, as well as a result of terminations of employment.