Net Income Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net income (loss)	$ 22,180	$ 17,928	$ 42,038	$ 35,480
Less net income allocated to participating securities:
Nonforfeitable dividends on participating securities	(98)	(126)	(199)	(249)
Income allocated to participating securities	(7)		(7)
Total net income allocated to participating securities	(105)	(126)	(206)	(249)
Less net income allocated to preferred stockholders:
Preferred stock dividends		(818)		(1,636)
Total net income allocated to preferred stockholders		(818)		(1,636)
Net income available to common stockholders	22,075	16,984	41,832	33,595
Effect of dilutive securities:
Participating securities	105
Convertible preferred securities		818		1,636
Total effect of dilutive securities	105	818		1,636
Net income for diluted net income per share	$ 22,180	$ 17,802	$ 41,832	$ 35,231
Shares for basic net income per share	37,969	35,299	37,707	35,288
Effect of dilutive securities:
Convertible preferred securities (in shares)		2,000		2,000
Total effect of dilutive securities (in shares)	195	2,012	13	2,014
Convertible preferred securities (in shares)		2,000		2,000
Weighted Average Number Diluted Shares Outstanding Adjustment, Total	195	2,012	13	2,014
Shares for diluted net income per share	38,164	37,311	37,720	37,302
Basic (in dollars per share)	$ 0.58	$ 0.48	$ 1.11	$ 0.95
Diluted (in dollars per share)	$ 0.58	$ 0.48	$ 1.11	$ 0.94
Stock options
Effect of dilutive securities:
Stock options and participating securities (in shares)	13	12	13	14
Participating Securities
Effect of dilutive securities:
Stock options and participating securities (in shares)	182