Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Amount [Abstract]
Restricted stock grants			$ 521	$ 920
Repurchase of common shares			(2,620)	(1,880)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance			418,811	404,345
Net income (loss)	$ (12,325)	$ 7,434	(9,508)	1,847
Other comprehensive income (loss)	(949)	2,679	(6,507)	11,947
Cash dividends paid to shareholders			(12,652)	(12,249)
Restricted stock grants			521	920
Repurchase of common shares			(2,620)	(1,880)
Ending balance	$ 388,045	$ 404,930	$ 388,045	$ 404,930
Class A [Member]
Shares [Abstract]
Balance, Beginning period (in shares)			2,623,109
Balance, Period end (in shares)	2,622,809		2,622,809
Class B [Member]
Shares [Abstract]
Balance, Beginning period (in shares)			12,423,518
Balance, Period end (in shares)	12,323,845		12,323,845
Common Stock [Member] | Class A [Member]
Shares [Abstract]
Balance, Beginning period (in shares)			2,623,109
Restricted stock grants (in shares)			0
Repurchase of common shares (in shares)			(300)
Balance, Period end (in shares)	2,622,809		2,622,809
Amount [Abstract]
Balance, Beginning period			$ 112
Restricted stock grants			0
Repurchase of common shares			0
Balance, Period end	$ 112		112
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants			0
Repurchase of common shares			$ 0
Common Stock [Member] | Class B [Member]
Shares [Abstract]
Balance, Beginning period (in shares)			12,423,518
Restricted stock grants (in shares)			12,502
Repurchase of common shares (in shares)			(112,175)
Balance, Period end (in shares)	12,323,845		12,323,845
Amount [Abstract]
Balance, Beginning period			$ 530
Restricted stock grants			1
Repurchase of common shares			(5)
Balance, Period end	$ 526		526
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants			1
Repurchase of common shares			(5)
Additional Paid-in Capital [Member]
Amount [Abstract]
Balance, Beginning period			55,078
Restricted stock grants			521
Repurchase of common shares			(484)
Balance, Period end	$ 55,115		55,115
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants			521
Repurchase of common shares			$ (484)