Condensed Consolidated Statement of Shareholders' Equity - 9 months ended Sep. 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	56,199				56,199
Fair value over carrying value of preferred shares subject to redemption	0	$ 2,257			(2,257)
Dividends declared to preferred shareholders	(3,656)				(3,656)
Proceeds from issuance of common shares for conversion of convertible notes	57,500		$ 24	57,476
Stock Issued During Period, Shares, New Issues			2,415,903
Stock Redeemed or Called During Period, Shares		(2,000)
Stock Repurchased and Retired During Period, Value	(50,420)	$ (50,420)
Stock options exercised, shares			342,661
Stock options exercised	4,791			(2,014)		6,805
Stock-based compensation expense	4,034			4,034
Deferral of executive and director compensation	351			351
Executive and director deferred compensation distributions shares			84,635
Executive and director deferred compensation distributions	0			(1,681)		1,681
Shares Outstanding, Ending Balance at Sep. 30, 2017		0	27,520,632
Stockholders' Equity, Ending Balance at Sep. 30, 2017	$ 722,973	$ 0	$ 295	$ 304,715	$ 457,447	$ (39,484)