Annual report pursuant to Section 13 and 15(d)

THREE-FOR-TWO STOCK SPLIT - Effects of Stock Split on Earnings Per Share (Details)

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THREE-FOR-TWO STOCK SPLIT - Effects of Stock Split on Earnings Per Share (Details) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 30, 2016
Mar. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]                        
Net Income $ 33,735 $ 51,430 $ 53,689 $ 40,270 $ 38,007 $ 49,651 $ 47,783 $ 31,928 $ 179,124 $ 167,369 $ 152,149 $ 137,664
Income per share—Basic (in dollars per share) $ 0.15 $ 0.24 $ 0.25 $ 0.18 $ 0.17 $ 0.23 $ 0.22 $ 0.15 $ 0.82 $ 0.77 $ 0.70 $ 0.63
Income per share—Diluted (in dollars per share) $ 0.15 $ 0.24 $ 0.25 $ 0.18 $ 0.17 $ 0.23 $ 0.22 $ 0.15 $ 0.82 $ 0.77 $ 0.70 $ 0.63
Shares used for computation:                        
Weighted average shares outstanding - basic (in shares)                 217,988 218,244 218,583 218,695
Weighted average shares outstanding - diluted (in shares)                 217,988 218,244 218,583 218,695
Pro forma                        
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]                        
Net Income                       $ 137,664
Income per share—Basic (in dollars per share)                       $ 0.94
Income per share—Diluted (in dollars per share)                       $ 0.94
Shares used for computation:                        
Weighted average shares outstanding - basic (in shares)                       145,796
Weighted average shares outstanding - diluted (in shares)                       145,796
Adjustment                        
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]                        
Net Income                       $ 0
Income per share—Basic (in dollars per share)                       $ (0.31)
Income per share—Diluted (in dollars per share)                       $ (0.31)
Shares used for computation:                        
Weighted average shares outstanding - basic (in shares)                       72,899
Weighted average shares outstanding - diluted (in shares)                       72,899