Earnings Per Share ("EPS") (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income available to common stockholders	$ 55,598	$ 53,562		$ 103,293	$ 104,874
Average common shares outstanding (in shares)	96,098	92,264		94,318	92,223
Average potential dilutive common shares (in shares)	270	469		270	469
Average diluted common shares (in shares)	96,368	92,733		94,588	92,692
Basic earnings per share (in dollars per share)	$ 0.58	$ 0.58		$ 1.10	$ 1.14
Diluted earnings per share (in dollars per share)	$ 0.58	$ 0.58	$ 0.58	$ 1.09	$ 1.13