Condensed Consolidated Statement of Shareholders' Equity - 6 months ended Jun. 30, 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	33,872				33,872
Dividends declared to preferred shareholders	(2,438)				(2,438)
Stock options exercised, shares			342,661
Stock options exercised	4,792			(2,014)		6,806
Stock-based compensation expense	2,566			2,566
Deferral of executive and director compensation	351			351
Executive and director deferred compensation distributions shares			84,458
Executive and director deferred compensation distributions	0			(1,677)		1,677
Shares Outstanding, Ending Balance at Jun. 30, 2017		2,000	25,104,552
Stockholders' Equity, Ending Balance at Jun. 30, 2017	$ 693,317	$ 48,163	$ 271	$ 245,775	$ 438,595	$ (39,487)