EPS Calculation (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Numerator:
Net income	$ 72,637	$ 83,011	$ 78,950	$ 78,070	$ 73,471	$ 79,510	$ 78,071	$ 82,174	$ 312,668	$ 313,226	$ 313,504
Dividends declared on preferred stock									(15,000)	(15,000)	(15,000)
Dividends, dividend equivalents and undistributed earnings allocated to participating securities									(1,628)	(1,539)	(1,106)
Net income available to common stockholders - basic and diluted									$ 296,040	$ 296,687	$ 297,398
Denominator:
Weighted average common shares for basic and diluted earnings per share									371,122	372,114	369,048	[1]
Basic and diluted earnings per share (in dollars per share)	$ 0.18	$ 0.21	$ 0.20	$ 0.20	$ 0.19	$ 0.20	$ 0.20	$ 0.21	$ 0.80	$ 0.80	$ 0.81
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									2,000
Restricted common stock
Denominator:
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									29
Weighted average grant date fair value (in dollars per share)	7.12								$ 7.12
Restricted Stock Units
Denominator:
Anti-dilutive securities excluded from diluted earnings per share calculations (in shares)									2,000
Weighted average grant date fair value (in dollars per share)	$ 6.85								$ 6.85

[1] At December 31, 2016, the Company had an aggregate of 2.0 million equity instruments outstanding that were not included in the calculation of diluted EPS for the year ended December 31, 2016, as their inclusion would have been anti-dilutive. These equity instruments were comprised of approximately 29,000 shares of restricted common stock with a weighted average grant date fair value of $7.12 and approximately $2.0 million RSUs with a weighted average grant date fair value of $6.85. These equity instruments may have a dilutive impact on future EPS.