Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]	$ 0
Unrealized losses arising during the period		(1,683)	$ 0
Change in unrealized gains on junior subordinated debentures carried at fair value, net of taxes		(1,253)	$ 0
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect on Retained Earnings, before Tax		13,000
Cumulative Effect of New Accounting Principle in Period of Adoption		9,700
Unrealized losses arising during the period		(1,700)
Change in unrealized gains on junior subordinated debentures carried at fair value, net of taxes		$ (1,300)

[1] The cumulative effect adjustment from retained earnings to accumulated other comprehensive income (loss) relating to the implementation of new accounting guidance for the junior subordinated debentures that the Company previously elected to fair value on a recurring basis. Refer to Note 1 for discussion of the new accounting guidance.