Summary of Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Net income available to common shareholders		$ 215,713	$ 92,940	$ 96,790
Average common shares outstanding (in shares)		92,268	69,385	61,291
Average potential dilutive common shares (in shares)		562	468	636
Average diluted common shares (in shares)		92,830	69,853	61,927
Basic earnings per share (in dollars per share)	[1]	$ 2.34	$ 1.34	$ 1.58
Diluted earnings per share (in dollars per share)	[1]	$ 2.32	$ 1.33	$ 1.56

[1] Per share amounts for the years ended 2017 and 2016 have been restated to reflect the effect of the two-for-one stock split on February 8, 2018.