Acquisition of South Pacific Financial Corporation - Supplemental Pro Forma Information (Details) - South Pacific Financial Corporation [Member] - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Operating revenues	$ 465,469	$ 519,452	$ 921,333	$ 892,820
Net income available to common stockholders	$ 10,271	$ 22,532	$ 17,147	$ 31,260
Income per share - basic (in USD per share)	$ 0.27	$ 0.59	$ 0.45	$ 0.82
Income per share - diluted (in USD per share)	$ 0.26	$ 0.57	$ 0.44	$ 0.79