Net Earnings Per Share (Details) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) item $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares
Anti-dilutive securities
Number of classes of common stock | item							2
Numerator
Preferred stock dividends	$ (3,844)						$ (8,115)
Net income available to common stockholders	$ 151,943			$ 146,574			$ 414,071	$ 372,436
Denominator
Weighted-average common shares outstanding | shares	112,133,556			104,066,785			111,511,960	103,940,723
Basic earnings per share (in dollars per share) | $ / shares	$ 1.36			$ 1.41			$ 3.71	$ 3.58
Numerator
Net income	$ 155,787	$ 128,305	$ 138,094	$ 146,574	$ 115,211	$ 110,651	$ 422,186	$ 372,436
Preferred dividends paid							(8,115)
Assumed conversion of convertible senior notes				1,823				5,309
Net income plus assumed conversions	$ 151,943			$ 148,397			$ 414,071	$ 377,745
Denominator
Number of shares used in basic computation | shares	112,133,556			104,066,785			111,511,960	103,940,723
Weighted-average effect of dilutive securities (in shares) | shares	1,129,840			8,442,827			1,325,566	8,437,147
Number of shares used in per share computation | shares	113,263,396			112,509,612			112,837,526	112,377,870
Diluted net income per share (in dollars per share) | $ / shares	$ 1.34			$ 1.32			$ 3.67	$ 3.36
Restricted Stock Units
Anti-dilutive securities
Anti-dilutive securities excluded from the computation of diluted earnings per share (in shares) | shares							946,406	950,761