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, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015		Sep. 30, 2015		Jun. 30, 2015		Mar. 31, 2015		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Basic earnings allocated to common shareholders																		$ 103,310		$ 97,577		$ 80,637
Net income		$ 30,718		$ 27,484		$ 25,405		$ 21,259		$ 26,740		$ 25,780		$ 21,946		$ 24,361		104,866		98,827		81,574
Earnings allocated to participating securities - preferred shares																		185		175		157
Earnings allocated to participating securities - nonvested restricted shares																		$ 1,371		$ 1,075		$ 780
Weighted average common shares outstanding																		57,184		57,019		52,618
Basic earnings per common share		$ 0.53	[1]	$ 0.47	[1]	$ 0.44	[1]	$ 0.37	[1]	$ 0.46	[1]	$ 0.45	[1]	$ 0.38	[1]	$ 0.42	[1]	$ 1.81	[1]	$ 1.71	[1]	$ 1.53
Earnings allocated to common shareholders, Diluted	[2]																	$ 103,310		$ 97,577		$ 80,640
Weighted average number of common shares outstanding																		57,184		57,019		52,618
Dilutive effect of equity awards and warrants																		9		13		565
Weighted average diluted common shares outstanding																		57,193		57,032		53,183
Diluted earnings per common share		$ 0.53	[1]	$ 0.47	[1]	$ 0.44	[1]	$ 0.37	[1]	$ 0.46	[1]	$ 0.45	[1]	$ 0.38	[1]	$ 0.42	[1]	$ 1.81	[1]	$ 1.71	[1]	$ 1.52
Potentially dilutive share options that were not included in the computation of diluted EPS because to do so would be anti-dilutive.																		19		37		64

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

[2] Earnings allocated to common shareholders for basic and diluted EPS may differ under the two-class method as a result of adding common stock equivalents for options and warrants to dilutive shares outstanding, which alters the ratio used to allocate earnings to common shareholders and participating securities for the purposes of calculating diluted EPS.