Condensed Consolidated Statement of Shareholders' Equity - 3 months ended Mar. 31, 2017 - 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, 2016		2,000	24,677,433
Stockholders' Equity, Beginning Balance at Dec. 31, 2016	$ 654,174	$ 48,163	$ 271	$ 246,549	$ 407,161	$ (47,970)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,883				16,883
Dividends declared to preferred shareholders	(1,219)				(1,219)
Stock options exercised, shares			37,326
Stock options exercised	496			(245)		741
Stock-based compensation expense	1,028			1,028
Deferral of executive and director compensation	350			350
Executive and director deferred compensation distributions shares			80,033
Executive and director deferred compensation distributions	0			(1,590)		1,590
Shares Outstanding, Ending Balance at Mar. 31, 2017		2,000	24,794,792
Stockholders' Equity, Ending Balance at Mar. 31, 2017	$ 671,712	$ 48,163	$ 271	$ 246,092	$ 422,825	$ (45,639)