Shareholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amount [Abstract]
Restricted stock grants	$ 478	$ 481
Repurchase of common shares	(235)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	418,811	404,345
Net income	330	6,756
Other comprehensive income (loss)	(3,344)	5,400
Cash dividends paid to shareholders	(4,229)	(4,080)
Restricted stock grants	478	481
Repurchase of common shares	(235)
Ending balance	$ 411,811	$ 412,902
Class A [Member]
Shares [Abstract]
Balance, Beginning period (in shares)	2,623,109
Balance, Period end (in shares)	2,623,109
Class B [Member]
Shares [Abstract]
Balance, Beginning period (in shares)	12,423,518
Balance, Period end (in shares)	12,418,082
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)	0
Balance, Period end (in shares)	2,623,109
Amount [Abstract]
Balance, Beginning period	$ 112
Restricted stock grants	0
Repurchase of common shares	0
Balance, Period end	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)	5,064
Repurchase of common shares (in shares)	(10,500)
Balance, Period end (in shares)	12,418,082
Amount [Abstract]
Balance, Beginning period	$ 530
Restricted stock grants	0
Repurchase of common shares	0
Balance, Period end	530
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants	0
Repurchase of common shares	0
Additional Paid-in Capital [Member]
Amount [Abstract]
Balance, Beginning period	55,078
Restricted stock grants	478
Repurchase of common shares	(45)
Balance, Period end	55,511
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Restricted stock grants	478
Repurchase of common shares	$ (45)