SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Basic EPS, Income (Numerator)
Income available to common shareholders									$ 191,642	$ 64,179	$ 105,028
Diluted EPS, Income (Numerator)
Income available to common shareholders									$ 191,642	$ 64,179	$ 105,028
Basic EPS, Weighted Average Shares (Denominator)
Number of shares outstanding									44,734	44,358	44,033
Effect of Dilutive Securities, Shares (Denominator)
Stock options (in shares)									523	477	467
Diluted EPS, Weighted Average Shares (Denominator)
Number of shares outstanding									45,257	44,835	44,500
Basic EPS, Per Share Amount
Basic net earnings per share (in dollars per share)	$ 1.19	$ 0.72	$ 0.91	$ 1.47	$ (0.46)	$ 0.89	$ 0.75	$ 0.28	$ 4.28	$ 1.45	$ 2.39
Diluted EPS, Per Share Amount
Diluted earnings per share (in dollars per share)	$ 1.18	$ 0.71	$ 0.89	$ 1.46	$ (0.46)	$ 0.88	$ 0.74	$ 0.27	$ 4.23	$ 1.43	$ 2.36