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Stock-based Compensation - Restricted Stock Units (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Restricted Stock Units (RSUs) [Member]      
Non-vested RSU's, beginning balance (in shares) 502,658    
Non-vested RSU's, weighted-average grant-date fair value, beginning balance (in dollars per share) $ 24.93    
Granted RSU's (in shares) 263,574 280,590 276,900
Granted RSU's, weighted-average grant-date fair value (in dollars per share) $ 22.38    
Vested RSU's (in shares) (307,207)    
Vested RSU's, weighted-average grant-date fair value (in dollars per share) $ 23.47    
Forfeited RSU's (in shares) (30,730)    
Forfeited RSU's, weighted-average grant-date fair value (in dollars per share) $ 24.76    
Non-vested RSU's, ending balance (in shares) 428,295 502,658  
Non-vested RSU's, weighted-average grant-date fair value, ending balance (in dollars per share) $ 24.42 $ 24.93  
Vested RSU's but unissued (in shares) 257,372    
Vested RSU's but unissued, weighted-average grant-date fair value (in dollars per share) $ 24.62    
Performance-based Restricted Stock Units [Member]      
Granted RSU's (in shares) 67,352    
Granted RSU's, weighted-average grant-date fair value (in dollars per share) $ 22.38    
Vested RSU's (in shares) (33,166)    
Vested RSU's, weighted-average grant-date fair value (in dollars per share) $ 22.38    
Non-vested RSU's, ending balance (in shares) 34,186    
Non-vested RSU's, weighted-average grant-date fair value, ending balance (in dollars per share) $ 22.38    
Vested RSU's but unissued (in shares) 27,366    
Vested RSU's but unissued, weighted-average grant-date fair value (in dollars per share) $ 22.38