Earnings Per Share Calculations (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share Calculations
Net income available to common stockholders	$ 13,510	$ 12,965	$ 12,437	$ 14,050
Weighted average common shares, basic	47,729,000	41,911,000	45,004,000	41,877,000
Dilutive shares	31,000		30,000
Shares used for dilutive computation	47,760,000	41,911,000	45,034,000	41,877,000
Net income per share - basic (in dollars per share)	$ 0.28	$ 0.31	$ 0.28	$ 0.34
Net income per share - diluted (in dollars per share)	$ 0.28	$ 0.31	$ 0.28	$ 0.34
Earnings per share calculations
Dilutive shares	31,000		30,000
Stock Appreciation Rights
Earnings Per Share Calculations
Dilutive shares			333,856
Earnings per share calculations
Anti-dilutive shares				333,856
Dilutive shares			333,856