Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Treasury Shares [Member]
Shares Outstanding, Beginning Balance at Dec. 31, 2013		2,000	24,357,943
Stockholders' Equity, Beginning Balance at Dec. 31, 2013	$ 492,803	$ 48,163	$ 271	$ 236,060	$ 262,625	$ (54,316)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	50,789				50,789
Dividends paid to preferred shareholders	(4,875)				(4,875)
Stock options exercised, shares			147,619
Stock options exercised - value	1,944			(988)		2,932
Stock-based compensation expense	3,215			3,215
Deferral of executive and director compensation	419			419
Executive and director deferred compensation distributions shares			7,348
Executive and director deferred compensation distributions	0			(146)		146
Shares Outstanding, Ending Balance at Dec. 31, 2014		2,000	24,512,910
Stockholders' Equity, Ending Balance at Dec. 31, 2014	544,295	$ 48,163	$ 271	238,560	308,539	(51,238)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	51,763				51,763
Dividends paid to preferred shareholders	(4,875)				(4,875)
Stock options exercised, shares			72,640
Stock options exercised - value	1,035			(408)		1,443
Stock-based compensation expense	3,942			3,942
Deferral of executive and director compensation	406			406
Executive and director deferred compensation distributions shares			63,494
Executive and director deferred compensation distributions	0			(1,261)		1,261
Shares Outstanding, Ending Balance at Dec. 31, 2015		2,000	24,649,044
Stockholders' Equity, Ending Balance at Dec. 31, 2015	596,566	$ 48,163	$ 271	241,239	355,427	(48,534)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	56,609				56,609
Dividends paid to preferred shareholders	(4,875)				(4,875)
Adjustments to Additional Paid in Capital, Other	$ 269			269
Stock options exercised, shares	(14,600)		14,600
Stock options exercised - value	$ 182			(108)		290
Stock-based compensation expense	5,315			5,315
Deferral of executive and director compensation	108			108
Executive and director deferred compensation distributions shares			13,789
Executive and director deferred compensation distributions	0			(274)		274
Shares Outstanding, Ending Balance at Dec. 31, 2016		2,000	24,677,433
Stockholders' Equity, Ending Balance at Dec. 31, 2016	$ 654,174	$ 48,163	$ 271	$ 246,549	$ 407,161	$ (47,970)