Earnings Per Common Share (Schedule of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic earnings allocated to common shareholders																	$ 192,921		$ 170,990		$ 111,324
Net income	$ 46,129		$ 50,727		$ 51,724		$ 45,871		$ 44,748		$ 46,415		$ 41,749		$ 39,970		194,451		172,882		112,828
Earnings allocated to participating securities - preferred shares																	0		0		3
Earnings allocated to participating securities - nonvested restricted shares																	$ 1,530		$ 1,892		$ 1,501
Weighted average common shares outstanding																	71,999		72,385		59,882
Basic earnings per common share	$ 0.64	[1]	$ 0.70	[1]	$ 0.71	[1]	$ 0.63	[1]	$ 0.61	[1]	$ 0.63	[1]	$ 0.57	[1]	$ 0.55	[1]	$ 2.68	[1]	$ 2.36	[1]	$ 1.86
Earnings allocated to common shareholders, Diluted																	$ 192,921		$ 170,990		$ 111,324
Weighted average number of common shares outstanding																	71,999		72,385		59,882
Dilutive effect of equity awards and warrants																	33		5		6
Weighted average diluted common shares outstanding																	72,032		72,390		59,888
Diluted earnings per common share	$ 0.64	[1]	$ 0.70	[1]	$ 0.71	[1]	$ 0.63	[1]	$ 0.61	[1]	$ 0.63	[1]	$ 0.57	[1]	$ 0.55	[1]	$ 2.68	[1]	$ 2.36	[1]	$ 1.86
Potentially dilutive share options that were not included in the computation of diluted EPS because to do so would be anti-dilutive.																	8		4		13

[1] Due to averaging of shares, quarterly EPS may not add up to the totals reported for the full year.