NET INCOME PER SHARE - Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic net income per share:
Net income applicable to common stockholders	$ 30,960	$ 31,902	$ 45,740	$ 53,174
Weighted average common shares outstanding (in shares)	55,197	57,879	55,233	57,836
Basic net income per share (in usd per share)	$ 0.56	$ 0.55	$ 0.83	$ 0.92
Diluted net income per share:
Net income applicable to common stockholders	$ 30,960	$ 31,902	$ 45,740	$ 53,174
Dilutive shares from assumed conversion of convertible senior notes (in shares)	0	435	0	1,073
Dilutive stock options and restricted stock (in shares)	471	960	486	1,114
Diluted weighted average common shares outstanding (in shares)	55,668	59,274	55,719	60,023
Diluted net income per share (in usd per share)	$ 0.56	$ 0.54	$ 0.82	$ 0.89