Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at amortized cost	$ 347,701	$ 347,615	$ 383,206
Operating leases (less than)	2,300
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, at amortized cost	1,120	$ 1,120	$ 1,120
Accounting Standards Update 2016-09
Schedule of Available-for-sale Securities [Line Items]
Effect of change on net income (less than)	$ 45
Effect of change on earnings per share (in usd per share)	$ 0.01