Earnings per Share (EPS) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 47,951	$ 34,838
Net income available to common shareholders	$ 47,951	$ 34,838	$ 157,331
Basic earnings per share (in dollars per share)	$ 0.53	$ 0.39
Diluted earnings per share (in dollars per share)	$ 0.52	$ 0.38
Basic weighted average shares outstanding (in shares)	90,785	90,185
Dilutive effect of nonvested shares (in shares)	1,074	1,329
Diluted weighted average shares outstanding (in shares)	91,859	91,514