STOCKHOLDERS' EQUITY - Capital Stock (Details) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) $ / shares shares
Equity offering [Line Items]
Issuance of common stock		$ 767,718	$ 866,156
At-The-Market Equity Offering Program
Equity offering [Line Items]
Common stock authorized under equity offering program	$ 1,000,000	1,000,000	$ 1,000,000
Stock issued during period, shares, new issues, equity offering program | shares			1.6
Stock issued during period, gross proceeds per share, equity offering program | $ / shares			$ 64.15
Equity offering program, remaining authorized offering amount	$ 900,000	$ 900,000	$ 900,000
June 2019 Registered Public Offering
Equity offering [Line Items]
Stock issued during period, shares, new issues, equity offering program | shares	12.7
Stock issued during period, gross proceeds per share, equity offering program | $ / shares	$ 62.75