EPS Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net income	$ 63,805	$ 83,011	$ 221,799	$ 240,031
Dividends declared on preferred stock	(3,750)	(3,750)	(11,250)	(11,250)
Dividends, dividend equivalents and undistributed earnings allocated to participating securities	(409)	(442)	(1,299)	(1,255)
Net income to common stockholders - basic and diluted	$ 59,646	$ 78,819	$ 209,250	$ 227,526
Denominator:
Weighted average common shares for basic and diluted earnings per share (in shares)	396,698	373,141	385,282	373,011
Basic and diluted earnings per share (in dollars per share)	$ 0.15	$ 0.21	$ 0.54	$ 0.61
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)			2,500
Restricted shares of common stock
Denominator:
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)			4
Weighted average grant date fair value (in dollars per share)	7.12		$ 7.12
RSUs
Denominator:
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)			2,500
Weighted average grant date fair value (in dollars per share)	$ 6.49		$ 6.49