Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jan. 02, 2018
Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies [Line Items]
Equity securities, carrying value						$ 41,107
Tax cuts and jobs act, incomplete accounting, estimated income tax expense	$ 1,000			$ 2,000
Tax cuts and jobs act, incomplete accounting, change in provisional income tax expense related to deemed repatriation of Canadian earnings	$ 0			$ 1,800
Federal Statutory Tax Rate	21.00%		35.00%	21.00%	35.00%	35.00%
Maximum [Member]
Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies [Line Items]
Provisional information accounting incomplete measurement period				1 year
Accounting Standards Update 2014-09 [Member]
Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies [Line Items]
Cumulative effect of accounting standard adoption on retained earnings							$ 24,700
Percentage of cumulative effect of accounting standard adoption on retained earnings							1.70%
Accounting Standards Update 2016-01 [Member]
Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies [Line Items]
Cumulative effect of accounting standard adoption on increase retained earnings		$ 7,700
Decrease accumulated other comprehensive income (loss)		7,700
Pre-tax gains and losses in realized investment gains (losses)	$ 500			$ 1,400
Equity securities, carrying value	$ 1,400			$ 1,400
Accounting Standards Update 2018-02 [Member]
Description of Business, Basis of Presentation, and Summary of Significant Accounting Policies [Line Items]
Decrease to retained earnings due to accounting standard adoption to reclassify stranded tax effects from Tax Reform Act		$ 7,800