Subsequent Events (Details) - USD ($)				3 Months Ended
	Apr. 19, 2018	Feb. 11, 2014	Feb. 11, 2014	Mar. 31, 2018	Mar. 31, 2017
Subsequent Event [Line Items]
Quarterly dividend declared (in dollars per share)				$ 0.42	$ 0.28
Stock repurchase program, additional authorized amount		$ 20,000,000.0	$ 20,000,000
Stock repurchase program, remaining authorized repurchase amount				$ 2,300,000
Subsequent Event
Subsequent Event [Line Items]
Stock repurchase program, additional authorized amount	$ 30,000,000
Subsequent Event | Common Class A
Subsequent Event [Line Items]
Quarterly dividend declared (in dollars per share)	$ 0.03