EPS Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic EPS:
Net income	$ 93,040	$ 88,857	$ 70,395	$ 83,395	$ 181,897	$ 153,790
Dividends declared on preferred stock	(3,750)	$ (3,750)	(3,750)	$ (3,750)	(7,500)	(7,500)
Dividends, dividend equivalents and undistributed earnings allocated to participating securities	(276)		(241)		(532)	(460)
Net Income Available to Common Stock and Participating Securities	$ 89,014		$ 66,404		$ 173,865	$ 145,830
Basic weighted average common shares outstanding (in shares)	450,538		398,478		450,449	398,398
Basic EPS (usd per share)	$ 0.20		$ 0.17		$ 0.39	$ 0.36
Diluted EPS:
Net income to common stockholders - basic	$ 89,014		$ 66,404		$ 173,865	$ 145,830
Interest expense on Convertible Senior Notes	1,206		0		1,206	0
Net income to common stockholders - diluted	$ 90,220		$ 66,404		$ 175,071	$ 145,830
Basic weighted average common shares outstanding (in shares)	450,538		398,478		450,449	398,398
Effect of Assumed Convertible Senior Notes to Common Shares	8,898		0		4,474	0
Diluted weighted average common shares outstanding (in shares)	459,436		398,478		454,923	398,398
Diluted EPS (usd per share)	$ 0.20		$ 0.17		$ 0.38	$ 0.36
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)	2,400				2,400
RSUs
Diluted EPS:
Weighted average grant date fair value (in dollars per share)	$ 7.42				$ 7.42