Earnings per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Earnings per Share
Net income	$ 17,004	$ 12,976
Less net income allocated to participating securities:
Nonforfeitable dividends on participating securities	(103)	(98)
Total net income allocated to participating securities	(103)	(98)
Less net income allocated to preferred stockholders:
Preferred stock dividends	(818)	(818)
Total net income allocated to preferred stockholders	(818)	(818)
Net income available to common stockholders	16,083	12,060
Effect of dilutive securities:
Convertible preferred securities	818
Net income for diluted net income per share	$ 16,901	$ 12,060
Shares for basic net income per share	34,586	30,365
Effect of dilutive securities:
Stock options (in shares)	25	34
Convertible preferred securities (in shares)	2,000
Shares for diluted net income per share	36,611	30,399
Basic net income per share (in dollars per share)	$ 0.47	$ 0.40
Diluted net income per share (in dollars per share)	$ 0.46	$ 0.40