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Equity Incentive Plan (Tables)
 12 Months Ended
Dec. 31, 2017
Equity Incentive Plan  
Schedule of Share-based Payment Award, Equity Instruments Other Than Options, Valuation Assumptions [Table Text Block]
The fair value of the market-based awards was determined using a Monte Carlo simulation with the following assumptions:
 
2017
 
2016
 
2015
Volatility (1)
43.92
%
 
45.92
%
 
48.11
%
Dividend rate (2)
$
0.06

 
$
0.05

 
$
0.04

Risk-free interest rate
1.51
%
 
0.93
%
 
1.32
%
(1)
Based on the share price history.
(2)
Based on the dividend rate at the time of the award.
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]
A summary of the unvested shares of restricted stock and restricted stock units is as follows:
 
January 1
through
August 31,
 
For the
year ended
December 31,
 
For the
year ended
December 31,
 
2017
 
2016
 
2015
 
Number of
Shares
 
Weighted-Average
Grant Date
Fair
Value
 
Number of
Shares
 
Weighted-Average
Grant Date
Fair
Value
 
Number of
Shares
 
Weighted-Average
Grant Date
Fair
Value
Unvested at the beginning of the period
1,870,393

 
$
6.21

 
1,830,123

 
$
6.79

 
1,509,519

 
$
5.70

Granted
1,398,705

 
5.53

 
1,207,926

 
6.24

 
1,116,394

 
8.14

Vested
(2,241,683
)
 
6.52

 
(771,508
)
 
7.72

 
(793,540
)
 
6.61

Forfeited
(1,027,415
)
 
4.61

 
(396,148
)
 
6.04

 
(2,250
)
 
9.62

Unvested at the end of the period
—

 
$
—

 
1,870,393

 
$
6.21

 
1,830,123

 
$
6.79