Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Calculation of basic and diluted earnings per common share
Antidilutive outstanding stock options excluded from the weighted average shares outstanding for the diluted earnings per share calculation (in shares)	167	0
Net income available to common shareholders (in dollars)	$ 13,732	$ 4,290
Weighted average common shares - basic	32,635,000	32,127,000
Total weighted average shares - diluted	33,071,000	32,609,000
Basic earnings per common share (in dollars per share)	$ 0.42	$ 0.13
Earnings per common share - diluted	$ 0.42	$ 0.13
Composition of basic outstanding shares
Weighted average shares outstanding - basic	32,123,000	31,686,000
Weighted average shares attributable to deferred compensation plans	512,000	441,000
Total weighted average shares - basic	32,635,000	32,127,000
Composition of diluted outstanding shares
Weighted average common shares - basic	32,635,000	32,127,000
Incremental weighted average shares attributable to deferred compensation plans	259,000	248,000
Weighted average shares attributable to stock options	177,000	180,000
Incremental Shares from stock option plan		54,000
Total weighted average shares - diluted	33,071,000	32,609,000