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Stock-Based Compensation - Schedule of Restricted Units (Details) - Restricted Stock Units - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Summary of restricted stock award activity (in shares)      
Outstanding at beginning of period (in shares) 604,214 566,321 515,468
Granted and fully vested (in shares) 51,292 37,893 50,853
Issued (in shares) (230,068) 0 0
Forfeited (in shares) 0 0 0
Outstanding at end of period (in shares) 425,438 604,214 566,321
Weighted-Average Grant Date Fair Value per Share (in usd per share)      
Outstanding at beginning of period (in USD per share) $ 12.48 $ 10.75 $ 9.10
Granted and fully vested (USD per share) 27.87 38.28 27.53
Issued (USD per share) 13.45 0.00 0.00
Forfeited (in USD per share) 0.00 0.00 0.00
Outstanding at end of period (in USD per share) $ 13.81 $ 12.48 $ 10.75
Additional disclosures      
Aggregate intrinsic value $ 7.5